From 3591cb5b1f7df389f924188cd66e65fa373bd875 Mon Sep 17 00:00:00 2001
From: Hao Hou <haohou302@gmail.com>
Date: Sat, 30 Nov 2019 10:36:25 -0700
Subject: [PATCH 1/8] Start working on the discrete refactoring

---
 examples/normal-dist2.rs |   2 +
 src/coord/datetime.rs    |  94 ++++++++++++++++++----------
 src/coord/mod.rs         |   3 +-
 src/coord/numeric.rs     | 128 +++++++--------------------------------
 src/coord/ranged.rs      |  97 +++++++----------------------
 src/series/histogram.rs  | 107 ++++++++++----------------------
 6 files changed, 142 insertions(+), 289 deletions(-)

diff --git a/examples/normal-dist2.rs b/examples/normal-dist2.rs
index 6155ea65..72323aa3 100644
--- a/examples/normal-dist2.rs
+++ b/examples/normal-dist2.rs
@@ -6,6 +6,8 @@ use rand_xorshift::XorShiftRng;
 
 use num_traits::sign::Signed;
 
+fn main() {}
+#[cfg(feature = "disabled")]
 fn main() -> Result<(), Box<dyn std::error::Error>> {
     let sd = 0.60;
 
diff --git a/src/coord/datetime.rs b/src/coord/datetime.rs
index cb96f937..45340a0b 100644
--- a/src/coord/datetime.rs
+++ b/src/coord/datetime.rs
@@ -135,14 +135,20 @@ impl<Z: TimeZone> Ranged for RangedDate<Z> {
 }
 
 impl<Z: TimeZone> DiscreteRanged for RangedDate<Z> {
-    type RangeParameter = ();
-    fn get_range_parameter(&self) {}
-    fn next_value(this: &Date<Z>, _: &()) -> Date<Z> {
-        this.clone() + Duration::days(1)
+    fn size(&self) -> usize {
+        ((self.1.clone() - self.0.clone()).num_days().max(0) + 1) as usize
     }
 
-    fn previous_value(this: &Date<Z>, _: &()) -> Date<Z> {
-        this.clone() - Duration::days(1)
+    fn index_of(&self, value: &Date<Z>) -> Option<usize> {
+        let ret = (value.clone() - self.0.clone()).num_days();
+        if ret < 0 {
+            return None;
+        }
+        Some(ret as usize)
+    }
+
+    fn from_index(&self, index: usize) -> Option<Date<Z>> {
+        Some(self.0.clone() + Duration::days(index as i64))
     }
 }
 
@@ -267,28 +273,39 @@ impl<T: TimeValue + Clone> Ranged for Monthly<T> {
 }
 
 impl<T: TimeValue + Clone> DiscreteRanged for Monthly<T> {
-    type RangeParameter = ();
-    fn get_range_parameter(&self) {}
-    fn next_value(this: &T, _: &()) -> T {
-        let mut year = this.date_ceil().year();
-        let mut month = this.date_ceil().month();
-        month += 1;
-        if month == 13 {
-            month = 1;
-            year += 1;
+    fn size(&self) -> usize {
+        let (start_year, start_month) = {
+            let ceil = self.0.start.date_ceil();
+            (ceil.year(), ceil.month())
+        };
+        let (end_year, end_month) = {
+            let floor = self.0.end.date_floor();
+            (floor.year(), floor.month())
+        };
+        ((end_year - start_year).max(0) * 12 + (start_month as i32) + (end_month as i32 - 1) + 1).max(0) as usize
+    }
+
+    fn index_of(&self, value: &T) -> Option<usize> {
+        let this_year = value.date_floor().year();
+        let this_month = value.date_floor().month();
+
+        let start_year = self.0.start.date_ceil().year();
+        let start_month = self.0.start.date_ceil().month();
+
+        let ret = (this_year - start_year).max(0) * 12 + (1 - start_month as i32) + (this_month as i32 - 1);
+        if ret >= 0 {
+            return Some(ret as usize);
         }
-        T::earliest_after_date(this.timezone().ymd(year, month, this.date_ceil().day()))
+        None
     }
 
-    fn previous_value(this: &T, _: &()) -> T {
-        let mut year = this.clone().date_floor().year();
-        let mut month = this.clone().date_floor().month();
-        month -= 1;
-        if month == 0 {
-            month = 12;
-            year -= 1;
-        }
-        T::earliest_after_date(this.timezone().ymd(year, month, this.date_floor().day()))
+    fn from_index(&self, index: usize) -> Option<T> {
+        let index_from_start_year = index + (self.0.start.date_ceil().month() - 1) as usize;
+        let year = self.0.start.date_ceil().year() + index_from_start_year as i32 / 12;
+        let month = index_from_start_year % 12;
+        Some(T::earliest_after_date(
+            self.0.start.timezone().ymd(year, month as u32, self.0.start.date_ceil().day())
+        ))
     }
 }
 
@@ -380,14 +397,29 @@ impl<T: TimeValue + Clone> Ranged for Yearly<T> {
 }
 
 impl<T: TimeValue + Clone> DiscreteRanged for Yearly<T> {
-    type RangeParameter = ();
-    fn get_range_parameter(&self) {}
-    fn next_value(this: &T, _: &()) -> T {
-        T::earliest_after_date(this.timezone().ymd(this.date_floor().year() + 1, 1, 1))
+    fn size(&self) -> usize {
+        let year_start = self.0.start.date_ceil().year();
+        let year_end = self.0.end.date_floor().year();
+        (year_end - year_start + 1) as usize
+    }
+
+    fn index_of(&self, value: &T) -> Option<usize> {
+        let year_start = self.0.start.date_ceil().year();
+        let year_value = value.date_floor().year();
+        let ret = year_value - year_start;
+        if ret < 0 {
+            return None;
+        }
+        Some(ret as usize)
     }
 
-    fn previous_value(this: &T, _: &()) -> T {
-        T::earliest_after_date(this.timezone().ymd(this.date_ceil().year() - 1, 1, 1))
+    fn from_index(&self, index: usize) -> Option<T> {
+        let year = self.0.start.date_ceil().year() + index as i32;
+        let ret = T::earliest_after_date(self.0.start.timezone().ymd(year, 1, 1));
+        if ret.date_ceil() <= self.0.start.date_floor() {
+            return Some(self.0.start.clone())
+        }
+        Some(ret)
     }
 }
 
diff --git a/src/coord/mod.rs b/src/coord/mod.rs
index 0afafa32..77d0df1c 100644
--- a/src/coord/mod.rs
+++ b/src/coord/mod.rs
@@ -28,6 +28,7 @@ mod datetime;
 mod logarithmic;
 mod numeric;
 mod ranged;
+mod group_by;
 
 #[cfg(feature = "chrono")]
 pub use datetime::{IntoMonthly, IntoYearly, RangedDate, RangedDateTime, RangedDuration};
@@ -44,7 +45,7 @@ pub use ranged::make_partial_axis;
 
 pub use logarithmic::{LogCoord, LogRange, LogScalable};
 
-pub use numeric::group_integer_by::{GroupBy, ToGroupByRange};
+pub use group_by::{GroupBy, ToGroupByRange};
 use std::rc::Rc;
 use std::sync::Arc;
 
diff --git a/src/coord/numeric.rs b/src/coord/numeric.rs
index 6a9f72d2..bb375158 100644
--- a/src/coord/numeric.rs
+++ b/src/coord/numeric.rs
@@ -1,17 +1,32 @@
 use std::ops::Range;
+use std::convert::TryFrom;
 
 use super::{AsRangedCoord, DiscreteRanged, Ranged, ReversibleRanged};
 
 macro_rules! impl_discrete_trait {
     ($name:ident) => {
         impl DiscreteRanged for $name {
-            type RangeParameter = ();
-            fn get_range_parameter(&self) -> () {}
-            fn next_value(this: &Self::ValueType, _: &()) -> Self::ValueType {
-                return *this + 1;
+            fn size(&self) -> usize {
+                if &self.1 < &self.0 {
+                    return 0;
+                }
+                let values = self.1 - self.0;
+                (values + 1) as usize
             }
-            fn previous_value(this: &Self::ValueType, _: &()) -> Self::ValueType {
-                return *this - 1;
+
+            fn index_of(&self, value: &Self::ValueType) -> Option<usize> {
+                if value < &self.0 {
+                    return None;
+                }
+                let ret = value - self.0;
+                Some(ret as usize)
+            }
+
+            fn from_index(&self, index: usize) -> Option<Self::ValueType> {
+                if let Ok(index) = Self::ValueType::try_from(index){
+                    return Some(self.0 + index);
+                }
+                None
             }
         }
     };
@@ -256,107 +271,6 @@ impl_ranged_type_trait!(u128, RangedCoordu128);
 impl_ranged_type_trait!(isize, RangedCoordisize);
 impl_ranged_type_trait!(usize, RangedCoordusize);
 
-// TODO: Think about how to re-organize this part
-pub mod group_integer_by {
-    use super::Ranged;
-    use super::{AsRangedCoord, DiscreteRanged};
-    use num_traits::{FromPrimitive, PrimInt, ToPrimitive};
-    use std::ops::{Mul, Range};
-
-    /// The ranged value spec that needs to be grouped.
-    /// This is useful, for example, when we have an X axis is a integer and denotes days.
-    /// And we are expecting the tick mark denotes weeks, in this way we can make the range
-    /// spec grouping by 7 elements.
-    pub struct GroupBy<T>(T, T::ValueType)
-    where
-        T::ValueType: PrimInt + ToPrimitive + FromPrimitive + Mul,
-        T: Ranged;
-
-    /// The trait that provides method `Self::group_by` function which creates a
-    /// `GroupBy` decorated ranged value.
-    pub trait ToGroupByRange
-    where
-        Self: AsRangedCoord,
-        <Self as AsRangedCoord>::Value: PrimInt + ToPrimitive + FromPrimitive + Mul,
-        <<Self as AsRangedCoord>::CoordDescType as Ranged>::ValueType:
-            PrimInt + ToPrimitive + FromPrimitive + Mul,
-    {
-        /// Make a grouping ranged value, see the documentation for `GroupBy` for details.
-        ///
-        /// - `value`: The number of values we want to group it
-        /// - **return**: The newly created grouping range sepcification
-        fn group_by(
-            self,
-            value: <<Self as AsRangedCoord>::CoordDescType as Ranged>::ValueType,
-        ) -> GroupBy<<Self as AsRangedCoord>::CoordDescType> {
-            GroupBy(self.into(), value)
-        }
-    }
-
-    impl<T> ToGroupByRange for T
-    where
-        Self: AsRangedCoord,
-        <Self as AsRangedCoord>::Value: PrimInt + FromPrimitive + ToPrimitive + Mul,
-        <<Self as AsRangedCoord>::CoordDescType as Ranged>::ValueType:
-            PrimInt + FromPrimitive + ToPrimitive + Mul,
-    {
-    }
-
-    impl<T> AsRangedCoord for GroupBy<T>
-    where
-        T::ValueType: PrimInt + ToPrimitive + FromPrimitive + Mul,
-        T: Ranged,
-    {
-        type Value = T::ValueType;
-        type CoordDescType = Self;
-    }
-
-    impl<T> DiscreteRanged for GroupBy<T>
-    where
-        T::ValueType: PrimInt + ToPrimitive + FromPrimitive + Mul,
-        T: Ranged + DiscreteRanged,
-    {
-        type RangeParameter = <T as DiscreteRanged>::RangeParameter;
-        fn get_range_parameter(&self) -> Self::RangeParameter {
-            self.0.get_range_parameter()
-        }
-        fn previous_value(this: &Self::ValueType, param: &Self::RangeParameter) -> Self::ValueType {
-            <T as DiscreteRanged>::previous_value(this, param)
-        }
-        fn next_value(this: &Self::ValueType, param: &Self::RangeParameter) -> Self::ValueType {
-            <T as DiscreteRanged>::next_value(this, param)
-        }
-    }
-
-    impl<T> Ranged for GroupBy<T>
-    where
-        T::ValueType: PrimInt + ToPrimitive + FromPrimitive + Mul,
-        T: Ranged,
-    {
-        type ValueType = T::ValueType;
-        fn map(&self, value: &T::ValueType, limit: (i32, i32)) -> i32 {
-            self.0.map(value, limit)
-        }
-        fn range(&self) -> Range<T::ValueType> {
-            self.0.range()
-        }
-        fn key_points(&self, max_points: usize) -> Vec<T::ValueType> {
-            let actual_range = self.0.range();
-            let from = ((actual_range.start + self.1 - T::ValueType::from_u8(1).unwrap()) / self.1)
-                .to_isize()
-                .unwrap();
-            let to = (actual_range.end / self.1).to_isize().unwrap();
-            let logic_range: super::RangedCoordisize = (from..to).into();
-
-            logic_range
-                .key_points(max_points)
-                .into_iter()
-                .map(|x| T::ValueType::from_isize(x).unwrap() * self.1)
-                .collect()
-        }
-    }
-}
-
 #[cfg(test)]
 mod test {
     use super::*;
diff --git a/src/coord/ranged.rs b/src/coord/ranged.rs
index b7f3ffd7..5071aa68 100644
--- a/src/coord/ranged.rs
+++ b/src/coord/ranged.rs
@@ -177,15 +177,23 @@ pub trait DiscreteRanged
 where
     Self: Ranged,
 {
-    type RangeParameter;
-
-    fn get_range_parameter(&self) -> Self::RangeParameter;
+    /// Get the number of element in the range
+    /// Note: we assume that all the ranged discrete coordinate has finite value
+    ///
+    /// - **returns** The number of values in the range
+    fn size(&self) -> usize;
 
-    /// Get the smallest value that is larger than the `this` value
-    fn next_value(this: &Self::ValueType, param: &Self::RangeParameter) -> Self::ValueType;
+    /// Map a value to the index
+    ///
+    /// - `value`: The value to map
+    /// - **returns** The index of the value
+    fn index_of(&self, value: &Self::ValueType) -> Option<usize>;
 
-    /// Get the largest value that is smaller than `this` value
-    fn previous_value(this: &Self::ValueType, param: &Self::RangeParameter) -> Self::ValueType;
+    /// Reverse map the index to the value
+    ///
+    /// - `value`: The index to map
+    /// - **returns** The value
+    fn from_index(&self, index: usize) -> Option<Self::ValueType>;
 }
 
 /// The trait for the type that can be converted into a ranged coordinate axis
@@ -223,67 +231,6 @@ where
     }
 }
 
-impl<T: AsRangedCoord> IntoCentric for T
-where
-    T::CoordDescType: DiscreteRanged,
-    <Self::CoordDescType as Ranged>::ValueType: Eq,
-{
-}
-
-impl<D: DiscreteRanged + Clone> Clone for CentricDiscreteRange<D>
-where
-    <D as Ranged>::ValueType: Eq,
-{
-    fn clone(&self) -> Self {
-        Self(self.0.clone())
-    }
-}
-
-impl<D: DiscreteRanged> Ranged for CentricDiscreteRange<D>
-where
-    <D as Ranged>::ValueType: Eq,
-{
-    type ValueType = <D as Ranged>::ValueType;
-
-    fn map(&self, value: &Self::ValueType, limit: (i32, i32)) -> i32 {
-        let prev = <D as DiscreteRanged>::previous_value(&value, &self.0.get_range_parameter());
-        (self.0.map(&prev, limit) + self.0.map(value, limit)) / 2
-    }
-
-    fn key_points(&self, max_points: usize) -> Vec<Self::ValueType> {
-        self.0.key_points(max_points)
-    }
-
-    fn range(&self) -> Range<Self::ValueType> {
-        self.0.range()
-    }
-}
-
-impl<D: DiscreteRanged> DiscreteRanged for CentricDiscreteRange<D>
-where
-    <D as Ranged>::ValueType: Eq,
-{
-    type RangeParameter = <D as DiscreteRanged>::RangeParameter;
-    fn get_range_parameter(&self) -> Self::RangeParameter {
-        self.0.get_range_parameter()
-    }
-    fn next_value(this: &Self::ValueType, param: &Self::RangeParameter) -> Self::ValueType {
-        <D as DiscreteRanged>::next_value(this, param)
-    }
-
-    fn previous_value(this: &Self::ValueType, param: &Self::RangeParameter) -> Self::ValueType {
-        <D as DiscreteRanged>::previous_value(this, param)
-    }
-}
-
-impl<D: DiscreteRanged> AsRangedCoord for CentricDiscreteRange<D>
-where
-    <D as Ranged>::ValueType: Eq,
-{
-    type CoordDescType = Self;
-    type Value = <Self as Ranged>::ValueType;
-}
-
 /// This axis decorator will make the axis partially display on the axis.
 /// At some time, we want the axis only covers some part of the value.
 /// This decorator will have an additional display range defined.
@@ -345,16 +292,16 @@ where
     R: Ranged,
     <R as Ranged>::ValueType: Eq + Clone,
 {
-    type RangeParameter = <R as DiscreteRanged>::RangeParameter;
-    fn get_range_parameter(&self) -> Self::RangeParameter {
-        self.0.get_range_parameter()
+    fn size(&self) -> usize {
+        self.0.size()
     }
-    fn next_value(this: &Self::ValueType, param: &Self::RangeParameter) -> Self::ValueType {
-        <R as DiscreteRanged>::next_value(this, param)
+
+    fn index_of(&self, value: &R::ValueType) -> Option<usize> {
+        self.0.index_of(value)
     }
 
-    fn previous_value(this: &Self::ValueType, param: &Self::RangeParameter) -> Self::ValueType {
-        <R as DiscreteRanged>::previous_value(this, param)
+    fn from_index(&self, index: usize) -> Option<Self::ValueType> {
+        self.0.from_index(index)
     }
 }
 
diff --git a/src/series/histogram.rs b/src/series/histogram.rs
index 75c2fb2a..14354e35 100644
--- a/src/series/histogram.rs
+++ b/src/series/histogram.rs
@@ -1,5 +1,4 @@
 use std::collections::{hash_map::IntoIter as HashMapIter, HashMap};
-use std::hash::Hash;
 use std::marker::PhantomData;
 use std::ops::AddAssign;
 
@@ -20,32 +19,30 @@ impl HistogramType for Horizontal {}
 pub struct Histogram<'a, BR, A, Tag = Vertical>
 where
     BR: DiscreteRanged,
-    BR::ValueType: Eq + Hash,
     A: AddAssign<A> + Default,
     Tag: HistogramType,
 {
     style: Box<dyn Fn(&BR::ValueType, &A) -> ShapeStyle + 'a>,
     margin: u32,
-    iter: HashMapIter<BR::ValueType, A>,
-    baseline: Box<dyn Fn(BR::ValueType) -> A + 'a>,
-    br_param: BR::RangeParameter,
-    _p: PhantomData<(BR, Tag)>,
+    iter: HashMapIter<usize, A>,
+    baseline: Box<dyn Fn(&BR::ValueType) -> A + 'a>,
+    br: BR,
+    _p: PhantomData<Tag>,
 }
 
 impl<'a, BR, A, Tag> Histogram<'a, BR, A, Tag>
 where
-    BR: DiscreteRanged,
-    BR::ValueType: Eq + Hash,
+    BR: DiscreteRanged + Clone,
     A: AddAssign<A> + Default + 'a,
     Tag: HistogramType,
 {
-    fn empty(br_param: BR::RangeParameter) -> Self {
+    fn empty(br: &BR) -> Self {
         Self {
             style: Box::new(|_, _| GREEN.filled()),
             margin: 5,
             iter: HashMap::new().into_iter(),
             baseline: Box::new(|_| A::default()),
-            br_param,
+            br: br.clone(),
             _p: PhantomData,
         }
     }
@@ -75,7 +72,7 @@ where
     }
 
     /// Set a function that defines variant baseline
-    pub fn baseline_func(mut self, func: impl Fn(BR::ValueType) -> A + 'a) -> Self {
+    pub fn baseline_func(mut self, func: impl Fn(&BR::ValueType) -> A + 'a) -> Self {
         self.baseline = Box::new(func);
         self
     }
@@ -88,67 +85,29 @@ where
 
     /// Set the data iterator
     pub fn data<I: IntoIterator<Item = (BR::ValueType, A)>>(mut self, iter: I) -> Self {
-        let mut buffer = HashMap::<BR::ValueType, A>::new();
+        let mut buffer = HashMap::<usize, A>::new();
         for (x, y) in iter.into_iter() {
-            *buffer.entry(x).or_insert_with(Default::default) += y;
+            if let Some(x) = self.br.index_of(&x) {
+                *buffer.entry(x).or_insert_with(Default::default) += y;
+            }
         }
         self.iter = buffer.into_iter();
         self
     }
 }
 
-pub trait UseDefaultParameter: Default {
-    fn new() -> Self {
-        Default::default()
-    }
-}
-
-impl UseDefaultParameter for () {}
-
 impl<'a, BR, A> Histogram<'a, BR, A, Vertical>
 where
-    BR: DiscreteRanged,
-    BR::ValueType: Eq + Hash,
+    BR: DiscreteRanged + Clone,
     A: AddAssign<A> + Default + 'a,
 {
-    /// Create a new histogram series.
-    ///
-    /// - `iter`: The data iterator
-    /// - `margin`: The margin between bars
-    /// - `style`: The style of bars
-    ///
-    /// Returns the newly created histogram series
-    #[allow(clippy::redundant_closure)]
-    pub fn new<S: Into<ShapeStyle>, I: IntoIterator<Item = (BR::ValueType, A)>>(
-        iter: I,
-        margin: u32,
-        style: S,
-    ) -> Self
-    where
-        BR::RangeParameter: UseDefaultParameter,
-    {
-        let mut buffer = HashMap::<BR::ValueType, A>::new();
-        for (x, y) in iter.into_iter() {
-            *buffer.entry(x).or_insert_with(Default::default) += y;
-        }
-        let style = style.into();
-        Self {
-            style: Box::new(move |_, _| style.clone()),
-            margin,
-            iter: buffer.into_iter(),
-            baseline: Box::new(|_| A::default()),
-            br_param: BR::RangeParameter::new(),
-            _p: PhantomData,
-        }
-    }
-
     pub fn vertical<ACoord, DB: DrawingBackend + 'a>(
         parent: &ChartContext<DB, RangedCoord<BR, ACoord>>,
     ) -> Self
     where
         ACoord: Ranged<ValueType = A>,
     {
-        let dp = parent.as_coord_spec().x_spec().get_range_parameter();
+        let dp = parent.as_coord_spec().x_spec();
 
         Self::empty(dp)
     }
@@ -156,8 +115,7 @@ where
 
 impl<'a, BR, A> Histogram<'a, BR, A, Horizontal>
 where
-    BR: DiscreteRanged,
-    BR::ValueType: Eq + Hash,
+    BR: DiscreteRanged + Clone,
     A: AddAssign<A> + Default + 'a,
 {
     pub fn horizontal<ACoord, DB: DrawingBackend>(
@@ -166,7 +124,7 @@ where
     where
         ACoord: Ranged<ValueType = A>,
     {
-        let dp = parent.as_coord_spec().y_spec().get_range_parameter();
+        let dp = parent.as_coord_spec().y_spec();
         Self::empty(dp)
     }
 }
@@ -174,18 +132,18 @@ where
 impl<'a, BR, A> Iterator for Histogram<'a, BR, A, Vertical>
 where
     BR: DiscreteRanged,
-    BR::ValueType: Eq + Hash,
     A: AddAssign<A> + Default,
 {
     type Item = Rectangle<(BR::ValueType, A)>;
     fn next(&mut self) -> Option<Self::Item> {
-        if let Some((x, y)) = self.iter.next() {
-            let nx = BR::next_value(&x, &self.br_param);
-            let base = (self.baseline)(BR::previous_value(&nx, &self.br_param));
-            let style = (self.style)(&x, &y);
-            let mut rect = Rectangle::new([(x, y), (nx, base)], style);
-            rect.set_margin(0, 0, self.margin, self.margin);
-            return Some(rect);
+        while let Some((x, y)) = self.iter.next() {
+            if let Some((x, Some(nx))) = self.br.from_index(x).map(|v| (v, self.br.from_index(x + 1))) {
+                let base = (self.baseline)(&x);
+                let style = (self.style)(&x, &y);
+                let mut rect = Rectangle::new([(x, y), (nx, base)], style);
+                rect.set_margin(0, 0, self.margin, self.margin);
+                return Some(rect)
+            }
         }
         None
     }
@@ -194,19 +152,18 @@ where
 impl<'a, BR, A> Iterator for Histogram<'a, BR, A, Horizontal>
 where
     BR: DiscreteRanged,
-    BR::ValueType: Eq + Hash,
     A: AddAssign<A> + Default,
 {
     type Item = Rectangle<(A, BR::ValueType)>;
     fn next(&mut self) -> Option<Self::Item> {
-        if let Some((y, x)) = self.iter.next() {
-            let ny = BR::next_value(&y, &self.br_param);
-            // With this trick we can avoid the clone trait bound
-            let base = (self.baseline)(BR::previous_value(&ny, &self.br_param));
-            let style = (self.style)(&y, &x);
-            let mut rect = Rectangle::new([(x, y), (base, ny)], style);
-            rect.set_margin(self.margin, self.margin, 0, 0);
-            return Some(rect);
+        while let Some((y, x)) = self.iter.next() {
+            if let Some((y, Some(ny))) = self.br.from_index(y).map(|v| (v, self.br.from_index(y + 1))) {
+                let base = (self.baseline)(&y);
+                let style = (self.style)(&y, &x);
+                let mut rect = Rectangle::new([(x,y), (base, ny)], style);
+                rect.set_margin(0, 0, self.margin, self.margin);
+                return Some(rect);
+            }
         }
         None
     }

From 4a328d769adc945bea48bfa52bdf7e85b552e91e Mon Sep 17 00:00:00 2001
From: Hao Hou <haohou302@gmail.com>
Date: Sat, 30 Nov 2019 10:37:31 -0700
Subject: [PATCH 2/8] Add missing files

---
 src/coord/group_by.rs | 73 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 73 insertions(+)
 create mode 100644 src/coord/group_by.rs

diff --git a/src/coord/group_by.rs b/src/coord/group_by.rs
new file mode 100644
index 00000000..0a438642
--- /dev/null
+++ b/src/coord/group_by.rs
@@ -0,0 +1,73 @@
+use super::{Ranged, AsRangedCoord, DiscreteRanged};
+use super::numeric::RangedCoordusize;
+use std::ops::Range;
+
+/// The ranged value spec that needs to be grouped.
+/// This is useful, for example, when we have an X axis is a integer and denotes days.
+/// And we are expecting the tick mark denotes weeks, in this way we can make the range
+/// spec grouping by 7 elements.
+pub struct GroupBy<T:DiscreteRanged>(T, usize);
+
+/// The trait that provides method `Self::group_by` function which creates a
+/// `GroupBy` decorated ranged value.
+pub trait ToGroupByRange : AsRangedCoord + Sized
+where
+    Self::CoordDescType : DiscreteRanged
+{
+    /// Make a grouping ranged value, see the documentation for `GroupBy` for details.
+    ///
+    /// - `value`: The number of values we want to group it
+    /// - **return**: The newly created grouping range specification
+    fn group_by(
+        self,
+        value: usize,
+    ) -> GroupBy<<Self as AsRangedCoord>::CoordDescType> {
+        GroupBy(self.into(), value)
+    }
+}
+
+impl<T: AsRangedCoord + Sized> ToGroupByRange for T
+where
+    T::CoordDescType: DiscreteRanged
+{
+}
+
+impl<T:DiscreteRanged> AsRangedCoord for GroupBy<T>
+{
+    type Value = T::ValueType;
+    type CoordDescType = Self;
+}
+
+impl<T:DiscreteRanged> DiscreteRanged for GroupBy<T>
+{
+    fn size(&self) -> usize {
+        (self.0.size() + self.1 - 1) / self.1
+    }
+    fn index_of(&self, value: &Self::ValueType) -> Option<usize> {
+        self.0.index_of(value).map(|idx| idx / self.1)
+    }
+    fn from_index(&self, index: usize) -> Option<Self::ValueType> {
+        self.0.from_index(index * self.1)
+    }
+}
+
+impl<T:DiscreteRanged> Ranged for GroupBy<T>
+{
+    type ValueType = T::ValueType;
+    fn map(&self, value: &T::ValueType, limit: (i32, i32)) -> i32 {
+        self.0.map(value, limit)
+    }
+    fn range(&self) -> Range<T::ValueType> {
+        self.0.range()
+    }
+    fn key_points(&self, max_points: usize) -> Vec<T::ValueType> {
+        let range = 0..(self.0.size() + self.1 - 1) / self.1;
+        let logic_range: RangedCoordusize = range.into();
+
+        logic_range
+            .key_points(max_points)
+            .into_iter()
+            .map(|x| self.0.from_index(x * self.1).unwrap())
+            .collect()
+    }
+}
\ No newline at end of file

From c7b2aac7a9a741ce7e9d0718ae4d5a1839bbb54d Mon Sep 17 00:00:00 2001
From: Hao Hou <haohou302@gmail.com>
Date: Sat, 30 Nov 2019 14:04:02 -0700
Subject: [PATCH 3/8] New discrete coord trait now works!

---
 examples/histogram.rs     |   4 +-
 examples/normal-dist2.rs  |   4 +-
 src/coord/category.rs     |   7 +-
 src/coord/datetime.rs     |  27 +++----
 src/coord/discrete.rs     | 138 +++++++++++++++++++++++++++++++++
 src/coord/group_by.rs     |  33 +++-----
 src/coord/mod.rs          |  13 ++--
 src/coord/numeric.rs      |   4 +-
 src/coord/partial_axis.rs | 106 +++++++++++++++++++++++++
 src/coord/ranged.rs       | 157 --------------------------------------
 src/series/histogram.rs   |  23 ++++--
 11 files changed, 294 insertions(+), 222 deletions(-)
 create mode 100644 src/coord/discrete.rs
 create mode 100644 src/coord/partial_axis.rs

diff --git a/examples/histogram.rs b/examples/histogram.rs
index c33363f8..2fa6aeef 100644
--- a/examples/histogram.rs
+++ b/examples/histogram.rs
@@ -10,13 +10,13 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
         .y_label_area_size(40)
         .margin(5)
         .caption("Histogram Test", ("sans-serif", 50.0).into_font())
-        .build_ranged(0u32..10u32, 0u32..10u32)?;
+        .build_ranged((0u32..10u32).into_centric(), 0u32..10u32)?;
 
     chart
         .configure_mesh()
         .disable_x_mesh()
         .line_style_1(&WHITE.mix(0.3))
-        .x_label_offset(30)
+        //.x_label_offset(30)
         .y_desc("Count")
         .x_desc("Bucket")
         .axis_desc_style(("sans-serif", 15).into_font())
diff --git a/examples/normal-dist2.rs b/examples/normal-dist2.rs
index 72323aa3..eaebfdc5 100644
--- a/examples/normal-dist2.rs
+++ b/examples/normal-dist2.rs
@@ -6,8 +6,6 @@ use rand_xorshift::XorShiftRng;
 
 use num_traits::sign::Signed;
 
-fn main() {}
-#[cfg(feature = "disabled")]
 fn main() -> Result<(), Box<dyn std::error::Error>> {
     let sd = 0.60;
 
@@ -30,7 +28,7 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
         .set_label_area_size(LabelAreaPosition::Bottom, 60)
         .set_label_area_size(LabelAreaPosition::Right, 60)
         .build_ranged(-4f64..4f64, 0f64..0.1)?
-        .set_secondary_coord((-40i32..40i32).into_centric(), 0u32..500u32);
+        .set_secondary_coord(-40i32..40i32, 0u32..500u32);
 
     chart
         .configure_mesh()
diff --git a/src/coord/category.rs b/src/coord/category.rs
index 805bad2c..f6dc6864 100644
--- a/src/coord/category.rs
+++ b/src/coord/category.rs
@@ -2,7 +2,7 @@ use std::fmt;
 use std::ops::Range;
 use std::rc::Rc;
 
-use super::{AsRangedCoord, Ranged};
+use super::Ranged;
 
 /// The category coordinate
 pub struct Category<T: PartialEq> {
@@ -172,11 +172,6 @@ impl<T: PartialEq> Ranged for Category<T> {
     }
 }
 
-impl<T: PartialEq> AsRangedCoord for Category<T> {
-    type CoordDescType = Self;
-    type Value = Category<T>;
-}
-
 #[cfg(test)]
 mod test {
     use super::*;
diff --git a/src/coord/datetime.rs b/src/coord/datetime.rs
index 45340a0b..bc869b98 100644
--- a/src/coord/datetime.rs
+++ b/src/coord/datetime.rs
@@ -165,11 +165,6 @@ impl<Z: TimeZone> AsRangedCoord for Range<Date<Z>> {
 #[derive(Clone)]
 pub struct Monthly<T: TimeValue>(Range<T>);
 
-impl<T: TimeValue + Clone> AsRangedCoord for Monthly<T> {
-    type CoordDescType = Monthly<T>;
-    type Value = T;
-}
-
 impl<T: TimeValue + Clone> Ranged for Monthly<T> {
     type ValueType = T;
 
@@ -282,7 +277,8 @@ impl<T: TimeValue + Clone> DiscreteRanged for Monthly<T> {
             let floor = self.0.end.date_floor();
             (floor.year(), floor.month())
         };
-        ((end_year - start_year).max(0) * 12 + (start_month as i32) + (end_month as i32 - 1) + 1).max(0) as usize
+        ((end_year - start_year).max(0) * 12 + (start_month as i32) + (end_month as i32 - 1) + 1)
+            .max(0) as usize
     }
 
     fn index_of(&self, value: &T) -> Option<usize> {
@@ -292,7 +288,9 @@ impl<T: TimeValue + Clone> DiscreteRanged for Monthly<T> {
         let start_year = self.0.start.date_ceil().year();
         let start_month = self.0.start.date_ceil().month();
 
-        let ret = (this_year - start_year).max(0) * 12 + (1 - start_month as i32) + (this_month as i32 - 1);
+        let ret = (this_year - start_year).max(0) * 12
+            + (1 - start_month as i32)
+            + (this_month as i32 - 1);
         if ret >= 0 {
             return Some(ret as usize);
         }
@@ -303,9 +301,11 @@ impl<T: TimeValue + Clone> DiscreteRanged for Monthly<T> {
         let index_from_start_year = index + (self.0.start.date_ceil().month() - 1) as usize;
         let year = self.0.start.date_ceil().year() + index_from_start_year as i32 / 12;
         let month = index_from_start_year % 12;
-        Some(T::earliest_after_date(
-            self.0.start.timezone().ymd(year, month as u32, self.0.start.date_ceil().day())
-        ))
+        Some(T::earliest_after_date(self.0.start.timezone().ymd(
+            year,
+            month as u32,
+            self.0.start.date_ceil().day(),
+        )))
     }
 }
 
@@ -313,11 +313,6 @@ impl<T: TimeValue + Clone> DiscreteRanged for Monthly<T> {
 #[derive(Clone)]
 pub struct Yearly<T: TimeValue>(Range<T>);
 
-impl<T: TimeValue + Clone> AsRangedCoord for Yearly<T> {
-    type CoordDescType = Yearly<T>;
-    type Value = T;
-}
-
 fn generate_yearly_keypoints<T: TimeValue>(
     max_points: usize,
     mut start_year: i32,
@@ -417,7 +412,7 @@ impl<T: TimeValue + Clone> DiscreteRanged for Yearly<T> {
         let year = self.0.start.date_ceil().year() + index as i32;
         let ret = T::earliest_after_date(self.0.start.timezone().ymd(year, 1, 1));
         if ret.date_ceil() <= self.0.start.date_floor() {
-            return Some(self.0.start.clone())
+            return Some(self.0.start.clone());
         }
         Some(ret)
     }
diff --git a/src/coord/discrete.rs b/src/coord/discrete.rs
new file mode 100644
index 00000000..5169a8a3
--- /dev/null
+++ b/src/coord/discrete.rs
@@ -0,0 +1,138 @@
+use super::{AsRangedCoord, Ranged};
+use std::fmt::{Debug, Formatter, Result as FmtResult};
+use std::ops::Range;
+
+/// The trait indicates the coordinate is discrete, so that we can draw histogram on it
+pub trait DiscreteRanged
+where
+    Self: Ranged,
+{
+    /// Get the number of element in the range
+    /// Note: we assume that all the ranged discrete coordinate has finite value
+    ///
+    /// - **returns** The number of values in the range
+    fn size(&self) -> usize;
+
+    /// Map a value to the index
+    ///
+    /// - `value`: The value to map
+    /// - **returns** The index of the value
+    fn index_of(&self, value: &Self::ValueType) -> Option<usize>;
+
+    /// Reverse map the index to the value
+    ///
+    /// - `value`: The index to map
+    /// - **returns** The value
+    fn from_index(&self, index: usize) -> Option<Self::ValueType>;
+}
+
+/// The axis decorator that makes key-point in the center of the value range
+/// This is useful when we draw a histogram, since we want the axis value label
+/// to be shown in the middle of the range rather than exactly the location where
+/// the value mapped to.
+pub struct CentricDiscreteRange<D: DiscreteRanged>(D);
+
+impl<D: DiscreteRanged + Clone> Clone for CentricDiscreteRange<D> {
+    fn clone(&self) -> Self {
+        CentricDiscreteRange(self.0.clone())
+    }
+}
+
+/// The trait for types that can decorated by `CentricDiscreteRange` decorator
+pub trait IntoCentric: AsRangedCoord
+where
+    Self::CoordDescType: DiscreteRanged,
+{
+    /// Convert current ranged value into a centric ranged value
+    fn into_centric(self) -> CentricDiscreteRange<Self::CoordDescType> {
+        CentricDiscreteRange(self.into())
+    }
+}
+
+impl<R: AsRangedCoord> IntoCentric for R where R::CoordDescType: DiscreteRanged {}
+
+/// The value that used by the centric coordinate
+pub enum CentricValues<T> {
+    Exact(T),
+    CenterOf(T),
+    Last,
+}
+
+impl<D: Debug> Debug for CentricValues<D> {
+    fn fmt(&self, formatter: &mut Formatter) -> FmtResult {
+        match self {
+            CentricValues::Exact(value) => write!(formatter, "{:?}", value),
+            CentricValues::CenterOf(value) => write!(formatter, "{:?}", value),
+            CentricValues::Last => Ok(()),
+        }
+    }
+}
+
+impl<D: DiscreteRanged> Ranged for CentricDiscreteRange<D> {
+    type ValueType = CentricValues<D::ValueType>;
+
+    fn map(&self, value: &Self::ValueType, limit: (i32, i32)) -> i32 {
+        let margin = ((limit.1 - limit.0) as f32 / self.0.size() as f32).round() as i32;
+
+        match value {
+            CentricValues::Exact(coord) => self.0.map(coord, (limit.0, limit.1 - margin)),
+            CentricValues::CenterOf(coord) => {
+                let left = self.0.map(coord, (limit.0, limit.1 - margin));
+                if let Some(idx) = self.0.index_of(coord) {
+                    if idx + 1 < self.0.size() {
+                        let right = self.0.map(
+                            &self.0.from_index(idx + 1).unwrap(),
+                            (limit.0, limit.1 - margin),
+                        );
+                        return (left + right) / 2;
+                    }
+                }
+                left + margin / 2
+            }
+            CentricValues::Last => limit.1,
+        }
+    }
+
+    fn key_points(&self, max_points: usize) -> Vec<Self::ValueType> {
+        self.0
+            .key_points(max_points)
+            .into_iter()
+            .map(CentricValues::CenterOf)
+            .collect()
+    }
+
+    fn range(&self) -> Range<Self::ValueType> {
+        let range = self.0.range();
+        CentricValues::Exact(range.start)..CentricValues::Exact(range.end)
+    }
+}
+
+impl<D: DiscreteRanged> DiscreteRanged for CentricDiscreteRange<D> {
+    fn size(&self) -> usize {
+        self.0.size() + 1
+    }
+
+    fn index_of(&self, value: &Self::ValueType) -> Option<usize> {
+        match value {
+            CentricValues::Exact(value) => self.0.index_of(value),
+            CentricValues::CenterOf(value) => self.0.index_of(value),
+            CentricValues::Last => Some(self.0.size()),
+        }
+    }
+
+    fn from_index(&self, idx: usize) -> Option<Self::ValueType> {
+        if idx < self.0.size() {
+            self.0.from_index(idx).map(|x| CentricValues::Exact(x))
+        } else if idx == self.0.size() {
+            Some(CentricValues::Last)
+        } else {
+            None
+        }
+    }
+}
+
+impl<T> From<T> for CentricValues<T> {
+    fn from(this: T) -> CentricValues<T> {
+        CentricValues::Exact(this)
+    }
+}
diff --git a/src/coord/group_by.rs b/src/coord/group_by.rs
index 0a438642..c38275ef 100644
--- a/src/coord/group_by.rs
+++ b/src/coord/group_by.rs
@@ -1,45 +1,31 @@
-use super::{Ranged, AsRangedCoord, DiscreteRanged};
 use super::numeric::RangedCoordusize;
+use super::{AsRangedCoord, DiscreteRanged, Ranged};
 use std::ops::Range;
 
 /// The ranged value spec that needs to be grouped.
 /// This is useful, for example, when we have an X axis is a integer and denotes days.
 /// And we are expecting the tick mark denotes weeks, in this way we can make the range
 /// spec grouping by 7 elements.
-pub struct GroupBy<T:DiscreteRanged>(T, usize);
+pub struct GroupBy<T: DiscreteRanged>(T, usize);
 
 /// The trait that provides method `Self::group_by` function which creates a
 /// `GroupBy` decorated ranged value.
-pub trait ToGroupByRange : AsRangedCoord + Sized
+pub trait ToGroupByRange: AsRangedCoord + Sized
 where
-    Self::CoordDescType : DiscreteRanged
+    Self::CoordDescType: DiscreteRanged,
 {
     /// Make a grouping ranged value, see the documentation for `GroupBy` for details.
     ///
     /// - `value`: The number of values we want to group it
     /// - **return**: The newly created grouping range specification
-    fn group_by(
-        self,
-        value: usize,
-    ) -> GroupBy<<Self as AsRangedCoord>::CoordDescType> {
+    fn group_by(self, value: usize) -> GroupBy<<Self as AsRangedCoord>::CoordDescType> {
         GroupBy(self.into(), value)
     }
 }
 
-impl<T: AsRangedCoord + Sized> ToGroupByRange for T
-where
-    T::CoordDescType: DiscreteRanged
-{
-}
+impl<T: AsRangedCoord + Sized> ToGroupByRange for T where T::CoordDescType: DiscreteRanged {}
 
-impl<T:DiscreteRanged> AsRangedCoord for GroupBy<T>
-{
-    type Value = T::ValueType;
-    type CoordDescType = Self;
-}
-
-impl<T:DiscreteRanged> DiscreteRanged for GroupBy<T>
-{
+impl<T: DiscreteRanged> DiscreteRanged for GroupBy<T> {
     fn size(&self) -> usize {
         (self.0.size() + self.1 - 1) / self.1
     }
@@ -51,8 +37,7 @@ impl<T:DiscreteRanged> DiscreteRanged for GroupBy<T>
     }
 }
 
-impl<T:DiscreteRanged> Ranged for GroupBy<T>
-{
+impl<T: DiscreteRanged> Ranged for GroupBy<T> {
     type ValueType = T::ValueType;
     fn map(&self, value: &T::ValueType, limit: (i32, i32)) -> i32 {
         self.0.map(value, limit)
@@ -70,4 +55,4 @@ impl<T:DiscreteRanged> Ranged for GroupBy<T>
             .map(|x| self.0.from_index(x * self.1).unwrap())
             .collect()
     }
-}
\ No newline at end of file
+}
diff --git a/src/coord/mod.rs b/src/coord/mod.rs
index 77d0df1c..f66321f8 100644
--- a/src/coord/mod.rs
+++ b/src/coord/mod.rs
@@ -25,10 +25,12 @@ use crate::drawing::backend::BackendCoord;
 mod category;
 #[cfg(feature = "chrono")]
 mod datetime;
+mod discrete;
+mod group_by;
 mod logarithmic;
 mod numeric;
+mod partial_axis;
 mod ranged;
-mod group_by;
 
 #[cfg(feature = "chrono")]
 pub use datetime::{IntoMonthly, IntoYearly, RangedDate, RangedDateTime, RangedDuration};
@@ -36,12 +38,11 @@ pub use numeric::{
     RangedCoordf32, RangedCoordf64, RangedCoordi128, RangedCoordi32, RangedCoordi64,
     RangedCoordu128, RangedCoordu32, RangedCoordu64,
 };
-pub use ranged::{
-    AsRangedCoord, DiscreteRanged, IntoCentric, IntoPartialAxis, MeshLine, Ranged, RangedCoord,
-    ReversibleRanged,
-};
+pub use ranged::{AsRangedCoord, MeshLine, Ranged, RangedCoord, ReversibleRanged};
+
+pub use partial_axis::{make_partial_axis, IntoPartialAxis};
 
-pub use ranged::make_partial_axis;
+pub use discrete::{DiscreteRanged, IntoCentric};
 
 pub use logarithmic::{LogCoord, LogRange, LogScalable};
 
diff --git a/src/coord/numeric.rs b/src/coord/numeric.rs
index bb375158..9b51c1b5 100644
--- a/src/coord/numeric.rs
+++ b/src/coord/numeric.rs
@@ -1,5 +1,5 @@
-use std::ops::Range;
 use std::convert::TryFrom;
+use std::ops::Range;
 
 use super::{AsRangedCoord, DiscreteRanged, Ranged, ReversibleRanged};
 
@@ -23,7 +23,7 @@ macro_rules! impl_discrete_trait {
             }
 
             fn from_index(&self, index: usize) -> Option<Self::ValueType> {
-                if let Ok(index) = Self::ValueType::try_from(index){
+                if let Ok(index) = Self::ValueType::try_from(index) {
                     return Some(self.0 + index);
                 }
                 None
diff --git a/src/coord/partial_axis.rs b/src/coord/partial_axis.rs
new file mode 100644
index 00000000..290c6017
--- /dev/null
+++ b/src/coord/partial_axis.rs
@@ -0,0 +1,106 @@
+use super::{AsRangedCoord, DiscreteRanged, Ranged};
+use std::ops::Range;
+
+/// This axis decorator will make the axis partially display on the axis.
+/// At some time, we want the axis only covers some part of the value.
+/// This decorator will have an additional display range defined.
+pub struct PartialAxis<R: Ranged>(R, Range<R::ValueType>);
+
+/// The trait for the types that can be converted into a partial axis
+pub trait IntoPartialAxis: AsRangedCoord {
+    /// Make the partial axis
+    ///
+    /// - `axis_range`: The range of the axis to be displayed
+    /// - **returns**: The converted range specification
+    fn partial_axis(
+        self,
+        axis_range: Range<<Self::CoordDescType as Ranged>::ValueType>,
+    ) -> PartialAxis<Self::CoordDescType> {
+        PartialAxis(self.into(), axis_range)
+    }
+}
+
+impl<R: AsRangedCoord> IntoPartialAxis for R {}
+
+impl<R: Ranged + Clone> Clone for PartialAxis<R>
+where
+    <R as Ranged>::ValueType: Clone,
+{
+    fn clone(&self) -> Self {
+        PartialAxis(self.0.clone(), self.1.clone())
+    }
+}
+
+impl<R: Ranged> Ranged for PartialAxis<R>
+where
+    R::ValueType: Clone,
+{
+    type ValueType = R::ValueType;
+
+    fn map(&self, value: &Self::ValueType, limit: (i32, i32)) -> i32 {
+        self.0.map(value, limit)
+    }
+
+    fn key_points(&self, max_points: usize) -> Vec<Self::ValueType> {
+        self.0.key_points(max_points)
+    }
+
+    fn range(&self) -> Range<Self::ValueType> {
+        self.0.range()
+    }
+
+    fn axis_pixel_range(&self, limit: (i32, i32)) -> Range<i32> {
+        let left = self.map(&self.1.start, limit);
+        let right = self.map(&self.1.end, limit);
+
+        left.min(right)..left.max(right)
+    }
+}
+
+impl<R: DiscreteRanged> DiscreteRanged for PartialAxis<R>
+where
+    R: Ranged,
+    <R as Ranged>::ValueType: Eq + Clone,
+{
+    fn size(&self) -> usize {
+        self.0.size()
+    }
+
+    fn index_of(&self, value: &R::ValueType) -> Option<usize> {
+        self.0.index_of(value)
+    }
+
+    fn from_index(&self, index: usize) -> Option<Self::ValueType> {
+        self.0.from_index(index)
+    }
+}
+
+/// Make a partial axis based on the percentage of visible portion.
+/// We can use `into_partial_axis` to create a partial axis range specification.
+/// But sometimes, we want to directly specify the percentage visible to the user.
+///
+/// - `axis_range`: The range specification
+/// - `part`: The visible part of the axis. Each value is from [0.0, 1.0]
+/// - **returns**: The partial axis created from the input, or `None` when not possible
+pub fn make_partial_axis<T>(
+    axis_range: Range<T>,
+    part: Range<f64>,
+) -> Option<PartialAxis<<Range<T> as AsRangedCoord>::CoordDescType>>
+where
+    Range<T>: AsRangedCoord,
+    T: num_traits::NumCast + Clone,
+{
+    let left: f64 = num_traits::cast(axis_range.start.clone())?;
+    let right: f64 = num_traits::cast(axis_range.end.clone())?;
+
+    let full_range_size = (right - left) / (part.end - part.start);
+
+    let full_left = left - full_range_size * part.start;
+    let full_right = right + full_range_size * (1.0 - part.end);
+
+    let full_range: Range<T> = num_traits::cast(full_left)?..num_traits::cast(full_right)?;
+
+    let axis_range: <Range<T> as AsRangedCoord>::CoordDescType = axis_range.into();
+
+    Some(PartialAxis(full_range.into(), axis_range.range()))
+}
diff --git a/src/coord/ranged.rs b/src/coord/ranged.rs
index 5071aa68..a8a34339 100644
--- a/src/coord/ranged.rs
+++ b/src/coord/ranged.rs
@@ -172,30 +172,6 @@ impl<'a, X: Ranged, Y: Ranged> MeshLine<'a, X, Y> {
     }
 }
 
-/// The trait indicates the coordinate is discrete, so that we can draw histogram on it
-pub trait DiscreteRanged
-where
-    Self: Ranged,
-{
-    /// Get the number of element in the range
-    /// Note: we assume that all the ranged discrete coordinate has finite value
-    ///
-    /// - **returns** The number of values in the range
-    fn size(&self) -> usize;
-
-    /// Map a value to the index
-    ///
-    /// - `value`: The value to map
-    /// - **returns** The index of the value
-    fn index_of(&self, value: &Self::ValueType) -> Option<usize>;
-
-    /// Reverse map the index to the value
-    ///
-    /// - `value`: The index to map
-    /// - **returns** The value
-    fn from_index(&self, index: usize) -> Option<Self::ValueType>;
-}
-
 /// The trait for the type that can be converted into a ranged coordinate axis
 pub trait AsRangedCoord: Sized {
     type CoordDescType: Ranged<ValueType = Self::Value> + From<Self>;
@@ -205,140 +181,7 @@ pub trait AsRangedCoord: Sized {
 impl<T> AsRangedCoord for T
 where
     T: Ranged,
-    Range<T::ValueType>: Into<T>,
 {
     type CoordDescType = T;
     type Value = T::ValueType;
 }
-
-/// The axis decorator that makes key-point in the center of the value range
-/// This is useful when we draw a histogram, since we want the axis value label
-/// to be shown in the middle of the range rather than exactly the location where
-/// the value mapped to.
-pub struct CentricDiscreteRange<D: DiscreteRanged>(D)
-where
-    <D as Ranged>::ValueType: Eq;
-
-/// The trait for types that can decorated by `CentricDiscreteRange` decorator
-pub trait IntoCentric: AsRangedCoord
-where
-    Self::CoordDescType: DiscreteRanged,
-    <Self::CoordDescType as Ranged>::ValueType: Eq,
-{
-    /// Convert current ranged value into a centric ranged value
-    fn into_centric(self) -> CentricDiscreteRange<Self::CoordDescType> {
-        CentricDiscreteRange(self.into())
-    }
-}
-
-/// This axis decorator will make the axis partially display on the axis.
-/// At some time, we want the axis only covers some part of the value.
-/// This decorator will have an additional display range defined.
-pub struct PartialAxis<R: Ranged>(R, Range<R::ValueType>);
-
-/// The trait for the types that can be converted into a partial axis
-pub trait IntoPartialAxis: AsRangedCoord {
-    /// Make the partial axis
-    ///
-    /// - `axis_range`: The range of the axis to be displayed
-    /// - **returns**: The converted range specification
-    fn partial_axis(
-        self,
-        axis_range: Range<<Self::CoordDescType as Ranged>::ValueType>,
-    ) -> PartialAxis<Self::CoordDescType> {
-        PartialAxis(self.into(), axis_range)
-    }
-}
-
-impl<R: AsRangedCoord> IntoPartialAxis for R {}
-
-impl<R: Ranged + Clone> Clone for PartialAxis<R>
-where
-    <R as Ranged>::ValueType: Clone,
-{
-    fn clone(&self) -> Self {
-        PartialAxis(self.0.clone(), self.1.clone())
-    }
-}
-
-impl<R: Ranged> Ranged for PartialAxis<R>
-where
-    R::ValueType: Clone,
-{
-    type ValueType = R::ValueType;
-
-    fn map(&self, value: &Self::ValueType, limit: (i32, i32)) -> i32 {
-        self.0.map(value, limit)
-    }
-
-    fn key_points(&self, max_points: usize) -> Vec<Self::ValueType> {
-        self.0.key_points(max_points)
-    }
-
-    fn range(&self) -> Range<Self::ValueType> {
-        self.0.range()
-    }
-
-    fn axis_pixel_range(&self, limit: (i32, i32)) -> Range<i32> {
-        let left = self.map(&self.1.start, limit);
-        let right = self.map(&self.1.end, limit);
-
-        left.min(right)..left.max(right)
-    }
-}
-
-impl<R: DiscreteRanged> DiscreteRanged for PartialAxis<R>
-where
-    R: Ranged,
-    <R as Ranged>::ValueType: Eq + Clone,
-{
-    fn size(&self) -> usize {
-        self.0.size()
-    }
-
-    fn index_of(&self, value: &R::ValueType) -> Option<usize> {
-        self.0.index_of(value)
-    }
-
-    fn from_index(&self, index: usize) -> Option<Self::ValueType> {
-        self.0.from_index(index)
-    }
-}
-
-impl<R: Ranged> AsRangedCoord for PartialAxis<R>
-where
-    <R as Ranged>::ValueType: Clone,
-{
-    type CoordDescType = Self;
-    type Value = <Self as Ranged>::ValueType;
-}
-
-/// Make a partial axis based on the percentage of visible portion.
-/// We can use `into_partial_axis` to create a partial axis range specification.
-/// But sometimes, we want to directly specify the percentage visible to the user.
-///
-/// - `axis_range`: The range specification
-/// - `part`: The visible part of the axis. Each value is from [0.0, 1.0]
-/// - **returns**: The partial axis created from the input, or `None` when not possible
-pub fn make_partial_axis<T>(
-    axis_range: Range<T>,
-    part: Range<f64>,
-) -> Option<PartialAxis<<Range<T> as AsRangedCoord>::CoordDescType>>
-where
-    Range<T>: AsRangedCoord,
-    T: num_traits::NumCast + Clone,
-{
-    let left: f64 = num_traits::cast(axis_range.start.clone())?;
-    let right: f64 = num_traits::cast(axis_range.end.clone())?;
-
-    let full_range_size = (right - left) / (part.end - part.start);
-
-    let full_left = left - full_range_size * part.start;
-    let full_right = right + full_range_size * (1.0 - part.end);
-
-    let full_range: Range<T> = num_traits::cast(full_left)?..num_traits::cast(full_right)?;
-
-    let axis_range: <Range<T> as AsRangedCoord>::CoordDescType = axis_range.into();
-
-    Some(PartialAxis(full_range.into(), axis_range.range()))
-}
diff --git a/src/series/histogram.rs b/src/series/histogram.rs
index 14354e35..d4220e0b 100644
--- a/src/series/histogram.rs
+++ b/src/series/histogram.rs
@@ -84,10 +84,13 @@ where
     }
 
     /// Set the data iterator
-    pub fn data<I: IntoIterator<Item = (BR::ValueType, A)>>(mut self, iter: I) -> Self {
+    pub fn data<TB: Into<BR::ValueType>, I: IntoIterator<Item = (TB, A)>>(
+        mut self,
+        iter: I,
+    ) -> Self {
         let mut buffer = HashMap::<usize, A>::new();
         for (x, y) in iter.into_iter() {
-            if let Some(x) = self.br.index_of(&x) {
+            if let Some(x) = self.br.index_of(&x.into()) {
                 *buffer.entry(x).or_insert_with(Default::default) += y;
             }
         }
@@ -137,12 +140,16 @@ where
     type Item = Rectangle<(BR::ValueType, A)>;
     fn next(&mut self) -> Option<Self::Item> {
         while let Some((x, y)) = self.iter.next() {
-            if let Some((x, Some(nx))) = self.br.from_index(x).map(|v| (v, self.br.from_index(x + 1))) {
+            if let Some((x, Some(nx))) = self
+                .br
+                .from_index(x)
+                .map(|v| (v, self.br.from_index(x + 1)))
+            {
                 let base = (self.baseline)(&x);
                 let style = (self.style)(&x, &y);
                 let mut rect = Rectangle::new([(x, y), (nx, base)], style);
                 rect.set_margin(0, 0, self.margin, self.margin);
-                return Some(rect)
+                return Some(rect);
             }
         }
         None
@@ -157,10 +164,14 @@ where
     type Item = Rectangle<(A, BR::ValueType)>;
     fn next(&mut self) -> Option<Self::Item> {
         while let Some((y, x)) = self.iter.next() {
-            if let Some((y, Some(ny))) = self.br.from_index(y).map(|v| (v, self.br.from_index(y + 1))) {
+            if let Some((y, Some(ny))) = self
+                .br
+                .from_index(y)
+                .map(|v| (v, self.br.from_index(y + 1)))
+            {
                 let base = (self.baseline)(&y);
                 let style = (self.style)(&y, &x);
-                let mut rect = Rectangle::new([(x,y), (base, ny)], style);
+                let mut rect = Rectangle::new([(x, y), (base, ny)], style);
                 rect.set_margin(0, 0, self.margin, self.margin);
                 return Some(rect);
             }

From d58e801cc41ca819f55f15ccd37208bdcb3f0798 Mon Sep 17 00:00:00 2001
From: Hao Hou <haohou302@gmail.com>
Date: Sat, 30 Nov 2019 14:46:40 -0700
Subject: [PATCH 4/8] Implemente the value iterator for discrete coordinate and
 add test cases

---
 src/coord/datetime.rs | 44 +++++++++++++++++++++++++++++++++++++++----
 src/coord/discrete.rs | 40 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 80 insertions(+), 4 deletions(-)

diff --git a/src/coord/datetime.rs b/src/coord/datetime.rs
index bc869b98..829e2356 100644
--- a/src/coord/datetime.rs
+++ b/src/coord/datetime.rs
@@ -277,8 +277,11 @@ impl<T: TimeValue + Clone> DiscreteRanged for Monthly<T> {
             let floor = self.0.end.date_floor();
             (floor.year(), floor.month())
         };
-        ((end_year - start_year).max(0) * 12 + (start_month as i32) + (end_month as i32 - 1) + 1)
-            .max(0) as usize
+        ((end_year - start_year).max(0) * 12
+            + (1 - start_month as i32)
+            + (end_month as i32 - 1)
+            + 1)
+        .max(0) as usize
     }
 
     fn index_of(&self, value: &T) -> Option<usize> {
@@ -298,13 +301,16 @@ impl<T: TimeValue + Clone> DiscreteRanged for Monthly<T> {
     }
 
     fn from_index(&self, index: usize) -> Option<T> {
+        if index == 0 {
+            return Some(T::earliest_after_date(self.0.start.date_ceil()));
+        }
         let index_from_start_year = index + (self.0.start.date_ceil().month() - 1) as usize;
         let year = self.0.start.date_ceil().year() + index_from_start_year as i32 / 12;
         let month = index_from_start_year % 12;
         Some(T::earliest_after_date(self.0.start.timezone().ymd(
             year,
-            month as u32,
-            self.0.start.date_ceil().day(),
+            month as u32 + 1,
+            1,
         )))
     }
 }
@@ -978,4 +984,34 @@ mod test {
         assert!(max == min);
         assert_eq!(max, 3600 * 2);
     }
+
+    #[test]
+    fn test_date_discrete() {
+        let coord: RangedDate<Utc> = (Utc.ymd(2019, 1, 1)..Utc.ymd(2019, 12, 31)).into();
+        assert_eq!(coord.size(), 365);
+        assert_eq!(coord.index_of(&Utc.ymd(2019, 2, 28)), Some(31 + 28 - 1));
+        assert_eq!(coord.from_index(364), Some(Utc.ymd(2019, 12, 31)));
+    }
+
+    #[test]
+    fn test_monthly_discrete() {
+        let coord1 = (Utc.ymd(2019, 1, 10)..Utc.ymd(2019, 12, 31)).monthly();
+        let coord2 = (Utc.ymd(2019, 1, 10)..Utc.ymd(2020, 1, 1)).monthly();
+        assert_eq!(coord1.size(), 12);
+        assert_eq!(coord2.size(), 13);
+
+        for i in 1..=12 {
+            assert_eq!(coord1.from_index(i - 1).unwrap().month(), i as u32);
+        }
+    }
+
+    #[test]
+    fn test_yearly_discrete() {
+        let coord1 = (Utc.ymd(2000, 1, 10)..Utc.ymd(2019, 12, 31)).yearly();
+        assert_eq!(coord1.size(), 20);
+
+        for i in 0..20 {
+            assert_eq!(coord1.from_index(i).unwrap().year(), 2000 + i as i32);
+        }
+    }
 }
diff --git a/src/coord/discrete.rs b/src/coord/discrete.rs
index 5169a8a3..9254cf45 100644
--- a/src/coord/discrete.rs
+++ b/src/coord/discrete.rs
@@ -24,6 +24,15 @@ where
     /// - `value`: The index to map
     /// - **returns** The value
     fn from_index(&self, index: usize) -> Option<Self::ValueType>;
+
+    /// Return a iterator that iterates over the all possible values
+    ///
+    /// - **returns** The value iterator
+    fn values(&self) -> DiscreteValueIter<'_, Self> 
+        where Self:Sized
+    {
+        DiscreteValueIter(self, 0, self.size())
+    }
 }
 
 /// The axis decorator that makes key-point in the center of the value range
@@ -136,3 +145,34 @@ impl<T> From<T> for CentricValues<T> {
         CentricValues::Exact(this)
     }
 }
+
+pub struct DiscreteValueIter<'a, T: DiscreteRanged>(&'a T, usize, usize);
+
+impl <'a, T:DiscreteRanged> Iterator for DiscreteValueIter<'a, T> {
+    type Item = T::ValueType;
+    fn next(&mut self) -> Option<T::ValueType> {
+        if self.1 >= self.2 {
+            return None;
+        }
+        let idx = self.1;
+        self.1 += 1;
+        self.0.from_index(idx)
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    #[test]
+    fn test_value_iter() {
+        let range:crate::coord::numeric::RangedCoordi32 = (-10..10).into();
+
+        let values:Vec<_> = range.values().collect();
+
+        assert_eq!(21, values.len());
+
+        for (expected, value) in (-10..=10).zip(values) {
+            assert_eq!(expected, value)
+        }
+    }
+}

From e98fb25ef3c3a5ff17e183ed84184bc474af15f8 Mon Sep 17 00:00:00 2001
From: Hao Hou <haohou302@gmail.com>
Date: Sat, 30 Nov 2019 19:39:02 -0700
Subject: [PATCH 5/8] Add test cases

---
 Cargo.toml            |  1 -
 src/coord/discrete.rs | 36 +++++++++++++++++++++++++++++++-----
 src/coord/group_by.rs | 14 ++++++++++++++
 3 files changed, 45 insertions(+), 6 deletions(-)

diff --git a/Cargo.toml b/Cargo.toml
index 45dd2391..f6febe33 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -79,7 +79,6 @@ rand_distr = "0.2.2"
 criterion = "0.3.0"
 rayon = "1.2.0"
 rand_xorshift = "0.2.0"
-cpuprofiler = "*"
 
 [target.'cfg(target_arch = "wasm32")'.dev-dependencies]
 wasm-bindgen-test = "0.3.4"
diff --git a/src/coord/discrete.rs b/src/coord/discrete.rs
index 9254cf45..c113ef22 100644
--- a/src/coord/discrete.rs
+++ b/src/coord/discrete.rs
@@ -28,8 +28,9 @@ where
     /// Return a iterator that iterates over the all possible values
     ///
     /// - **returns** The value iterator
-    fn values(&self) -> DiscreteValueIter<'_, Self> 
-        where Self:Sized
+    fn values(&self) -> DiscreteValueIter<'_, Self>
+    where
+        Self: Sized,
     {
         DiscreteValueIter(self, 0, self.size())
     }
@@ -148,7 +149,7 @@ impl<T> From<T> for CentricValues<T> {
 
 pub struct DiscreteValueIter<'a, T: DiscreteRanged>(&'a T, usize, usize);
 
-impl <'a, T:DiscreteRanged> Iterator for DiscreteValueIter<'a, T> {
+impl<'a, T: DiscreteRanged> Iterator for DiscreteValueIter<'a, T> {
     type Item = T::ValueType;
     fn next(&mut self) -> Option<T::ValueType> {
         if self.1 >= self.2 {
@@ -165,9 +166,9 @@ mod test {
     use super::*;
     #[test]
     fn test_value_iter() {
-        let range:crate::coord::numeric::RangedCoordi32 = (-10..10).into();
+        let range: crate::coord::numeric::RangedCoordi32 = (-10..10).into();
 
-        let values:Vec<_> = range.values().collect();
+        let values: Vec<_> = range.values().collect();
 
         assert_eq!(21, values.len());
 
@@ -175,4 +176,29 @@ mod test {
             assert_eq!(expected, value)
         }
     }
+
+    #[test]
+    fn test_centric_coord() {
+        let coord = (0..10).into_centric();
+
+        assert_eq!(coord.size(), 12);
+        for i in 0..=11 {
+            match coord.from_index(i as usize) {
+                Some(CentricValues::Exact(value)) => assert_eq!(i, value),
+                Some(CentricValues::Last) => assert_eq!(i, 11),
+                _ => panic!(),
+            }
+        }
+
+        for (kps, idx) in coord.key_points(20).into_iter().zip(0..) {
+            match kps {
+                CentricValues::CenterOf(value) if value <= 10 => assert_eq!(value, idx),
+                _ => panic!(),
+            }
+        }
+
+        assert_eq!(coord.map(&CentricValues::CenterOf(0), (0, 24)), 1);
+        assert_eq!(coord.map(&CentricValues::Exact(0), (0, 24)), 0);
+        assert_eq!(coord.map(&CentricValues::Exact(1), (0, 24)), 2);
+    }
 }
diff --git a/src/coord/group_by.rs b/src/coord/group_by.rs
index c38275ef..5cda0fb8 100644
--- a/src/coord/group_by.rs
+++ b/src/coord/group_by.rs
@@ -56,3 +56,17 @@ impl<T: DiscreteRanged> Ranged for GroupBy<T> {
             .collect()
     }
 }
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    #[test]
+    fn test_group_by() {
+        let coord = (0..100).group_by(10);
+        assert_eq!(coord.size(), 11);
+        for (idx, val) in (0..).zip(coord.values()) {
+            assert_eq!(val, idx * 10);
+            assert_eq!(coord.from_index(idx as usize), Some(val));
+        }
+    }
+}

From 33444aa40cea694e648a1d35df27e89b40429b11 Mon Sep 17 00:00:00 2001
From: Hao Hou <haohou302@gmail.com>
Date: Sat, 30 Nov 2019 21:58:14 -0700
Subject: [PATCH 6/8] Add more test

---
 examples/histogram.rs | 1 -
 src/coord/datetime.rs | 5 +++++
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/examples/histogram.rs b/examples/histogram.rs
index 2fa6aeef..7e1d31f1 100644
--- a/examples/histogram.rs
+++ b/examples/histogram.rs
@@ -16,7 +16,6 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
         .configure_mesh()
         .disable_x_mesh()
         .line_style_1(&WHITE.mix(0.3))
-        //.x_label_offset(30)
         .y_desc("Count")
         .x_desc("Bucket")
         .axis_desc_style(("sans-serif", 15).into_font())
diff --git a/src/coord/datetime.rs b/src/coord/datetime.rs
index 829e2356..be4e75dc 100644
--- a/src/coord/datetime.rs
+++ b/src/coord/datetime.rs
@@ -1002,6 +1002,10 @@ mod test {
 
         for i in 1..=12 {
             assert_eq!(coord1.from_index(i - 1).unwrap().month(), i as u32);
+            assert_eq!(
+                coord1.index_of(&coord1.from_index(i - 1).unwrap()).unwrap(),
+                i - 1
+            );
         }
     }
 
@@ -1012,6 +1016,7 @@ mod test {
 
         for i in 0..20 {
             assert_eq!(coord1.from_index(i).unwrap().year(), 2000 + i as i32);
+            assert_eq!(coord1.index_of(&coord1.from_index(i).unwrap()).unwrap(), i);
         }
     }
 }

From d8b6cb3613f648746da8aa796e9f5e3a30a92c47 Mon Sep 17 00:00:00 2001
From: Hao Hou <haohou302@gmail.com>
Date: Sun, 1 Dec 2019 08:06:27 -0700
Subject: [PATCH 7/8] Add more test cases

---
 src/coord/numeric.rs      |  8 ++++++++
 src/coord/partial_axis.rs | 12 ++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/src/coord/numeric.rs b/src/coord/numeric.rs
index 9b51c1b5..e1f5cd8f 100644
--- a/src/coord/numeric.rs
+++ b/src/coord/numeric.rs
@@ -306,4 +306,12 @@ mod test {
         let _coord =
             RangedCoord::<RangedCoordu32, RangedCoordu32>::new(0..10, 0..10, (0..1024, 0..768));
     }
+
+    #[test]
+    fn test_coord_unmap() {
+        let coord: RangedCoordu32 = (0..20).into();
+        let pos = coord.map(&5, (1000, 2000));
+        let value = coord.unmap(pos, (1000, 2000));
+        assert_eq!(value, Some(5));
+    }
 }
diff --git a/src/coord/partial_axis.rs b/src/coord/partial_axis.rs
index 290c6017..e3e3a518 100644
--- a/src/coord/partial_axis.rs
+++ b/src/coord/partial_axis.rs
@@ -104,3 +104,15 @@ where
 
     Some(PartialAxis(full_range.into(), axis_range.range()))
 }
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    #[test]
+    fn test_make_partial_axis() {
+        let r = make_partial_axis(20..80, 0.2..0.8).unwrap();
+        assert_eq!(r.size(), 101);
+        assert_eq!(r.range(), 0..100);
+        assert_eq!(r.axis_pixel_range((0, 100)), 20..80);
+    }
+}

From 473adc50bf79121431facf91062764c78f8008e4 Mon Sep 17 00:00:00 2001
From: Hao Hou <haohou302@gmail.com>
Date: Sun, 1 Dec 2019 11:00:23 -0700
Subject: [PATCH 8/8] Add previous and next function to discrete trait

---
 src/coord/discrete.rs | 54 +++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 52 insertions(+), 2 deletions(-)

diff --git a/src/coord/discrete.rs b/src/coord/discrete.rs
index c113ef22..c63a3f40 100644
--- a/src/coord/discrete.rs
+++ b/src/coord/discrete.rs
@@ -2,7 +2,11 @@ use super::{AsRangedCoord, Ranged};
 use std::fmt::{Debug, Formatter, Result as FmtResult};
 use std::ops::Range;
 
-/// The trait indicates the coordinate is discrete, so that we can draw histogram on it
+/// The trait indicates the coordinate is discrete
+/// This means we can bidirectionally map the range value to 0 to N
+/// in which N is the number of distinct values of the range.
+///
+/// This is useful since for a histgoram, this is an abstraction of bucket.
 pub trait DiscreteRanged
 where
     Self: Ranged,
@@ -15,12 +19,18 @@ where
 
     /// Map a value to the index
     ///
+    /// Note: This function doesn't guareentee return None when the value is out of range.
+    /// The only way to confirm the value is in the range is to examing the return value isn't
+    /// larger than self.size.
+    ///
     /// - `value`: The value to map
     /// - **returns** The index of the value
     fn index_of(&self, value: &Self::ValueType) -> Option<usize>;
 
     /// Reverse map the index to the value
     ///
+    /// Note: This function doesn't guareentee returning None when the index is out of range.
+    ///
     /// - `value`: The index to map
     /// - **returns** The value
     fn from_index(&self, index: usize) -> Option<Self::ValueType>;
@@ -34,6 +44,42 @@ where
     {
         DiscreteValueIter(self, 0, self.size())
     }
+
+    /// Returns the previous value in this range
+    ///
+    /// Normally, it's based on the `from_index` and `index_of` function. But for
+    /// some of the coord spec, it's possible that we value faster implementation.
+    /// If this is the case, we can impelemnet the type specific impl for the `previous`
+    /// and `next`.
+    ///
+    /// - `value`: The current value
+    /// - **returns**: The value piror to current value
+    fn previous(&self, value: &Self::ValueType) -> Option<Self::ValueType> {
+        if let Some(idx) = self.index_of(value) {
+            if idx > 0 {
+                return self.from_index(idx - 1);
+            }
+        }
+        None
+    }
+
+    /// Returns the next value in this range
+    ///
+    /// Normally, it's based on the `from_index` and `index_of` function. But for
+    /// some of the coord spec, it's possible that we value faster implementation.
+    /// If this is the case, we can impelemnet the type specific impl for the `previous`
+    /// and `next`.
+    ///
+    /// - `value`: The current value
+    /// - **returns**: The value next to current value
+    fn next(&self, value: &Self::ValueType) -> Option<Self::ValueType> {
+        if let Some(idx) = self.index_of(value) {
+            if idx + 1 < self.size() {
+                return self.from_index(idx + 1);
+            }
+        }
+        None
+    }
 }
 
 /// The axis decorator that makes key-point in the center of the value range
@@ -173,8 +219,12 @@ mod test {
         assert_eq!(21, values.len());
 
         for (expected, value) in (-10..=10).zip(values) {
-            assert_eq!(expected, value)
+            assert_eq!(expected, value);
         }
+        assert_eq!(range.next(&5), Some(6));
+        assert_eq!(range.next(&10), None);
+        assert_eq!(range.previous(&-10), None);
+        assert_eq!(range.previous(&10), Some(9));
     }
 
     #[test]