Added Itertools::dedup_with_count() and Itertools::dedup_by_with_count().

Fixes #393.

Author: orium

src/adaptors/mod.rs

@@ -10,7 +10,7 @@ pub use self::multi_product::*;
 
 use std::fmt;
 use std::mem::replace;
-use std::iter::{Fuse, Peekable, FromIterator};
+use std::iter::{Fuse, Peekable, FromIterator, FusedIterator};
 use std::marker::PhantomData;
 use crate::size_hint;
 
@@ -803,6 +803,88 @@ impl<I, Pred> Iterator for DedupBy<I, Pred>
     }
 }
 
+/// An iterator adaptor that removes repeated duplicates, while keeping a count of how many
+/// repeated elements were present. This will determine equality using a comparison function.
+///
+/// See [`.dedup_by_with_count()`](../trait.Itertools.html#method.dedup_by_with_count) or
+/// [`.dedup_with_count()`](../trait.Itertools.html#method.dedup_with_count) for more information.
+#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
+pub struct DedupByWithCount<I, Pred>
+    where I: Iterator
+{
+    iter: Peekable<I>,
+    dedup_pred: Pred,
+}
+
+/// An iterator adaptor that removes repeated duplicates, while keeping a count of how many
+/// repeated elements were present.
+///
+/// See [`.dedup_with_count()`](../trait.Itertools.html#method.dedup_with_count) for more information.
+pub type DedupWithCount<I> = DedupByWithCount<I, DedupEq>;
+
+/// Create a new `DedupByWithCount`.
+pub fn dedup_by_with_count<I, Pred>(iter: I, dedup_pred: Pred) -> DedupByWithCount<I, Pred>
+    where I: Iterator,
+{
+    DedupByWithCount {
+        iter: iter.peekable(),
+        dedup_pred,
+    }
+}
+
+/// Create a new `DedupWithCount`.
+pub fn dedup_with_count<I>(iter: I) -> DedupWithCount<I>
+    where I: Iterator
+{
+    dedup_by_with_count(iter, DedupEq)
+}
+
+impl<I, Pred> fmt::Debug for DedupByWithCount<I, Pred>
+    where I: Iterator + fmt::Debug,
+          I::Item: fmt::Debug,
+{
+    debug_fmt_fields!(Dedup, iter);
+}
+
+impl<I: Clone, Pred: Clone> Clone for DedupByWithCount<I, Pred>
+    where I: Iterator,
+          I::Item: Clone,
+{
+    clone_fields!(iter, dedup_pred);
+}
+
+impl<I, Pred> Iterator for DedupByWithCount<I, Pred>
+    where I: Iterator,
+          Pred: DedupPredicate<I::Item>,
+{
+    type Item = (usize, I::Item);
+
+    fn next(&mut self) -> Option<(usize, I::Item)> {
+        self.iter.next().map(|base| {
+            let mut count: usize = 1;
+
+            while let Some(next) = self.iter.peek() {
+                if self.dedup_pred.dedup_pair(&base, next) {
+                    self.iter.next();
+                    count += 1;
+                } else {
+                    break;
+                }
+            }
+
+            (count, base)
+        })
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let (low, high) = self.iter.size_hint();
+
+        ((low > 0) as usize, high)
+    }
+}
+
+impl<I: Iterator, Pred: DedupPredicate<I::Item>> FusedIterator for DedupByWithCount<I, Pred> {}
+
 /// An iterator adaptor that borrows from a `Clone`-able iterator
 /// to only pick off elements while the predicate returns `true`.
 ///

src/lib.rs

@@ -78,6 +78,8 @@ pub mod structs {
     pub use crate::adaptors::{
         Dedup,
         DedupBy,
+        DedupWithCount,
+        DedupByWithCount,
         Interleave,
         InterleaveShortest,
         Product,
@@ -970,7 +972,7 @@ pub trait Itertools : Iterator {
     /// use itertools::Itertools;
     ///
     /// let data = vec![(0, 1.), (1, 1.), (0, 2.), (0, 3.), (1, 3.), (1, 2.), (2, 2.)];
-    /// itertools::assert_equal(data.into_iter().dedup_by(|x, y| x.1==y.1),
+    /// itertools::assert_equal(data.into_iter().dedup_by(|x, y| x.1 == y.1),
     ///                         vec![(0, 1.), (0, 2.), (0, 3.), (1, 2.)]);
     /// ```
     fn dedup_by<Cmp>(self, cmp: Cmp) -> DedupBy<Self, Cmp>
@@ -980,6 +982,50 @@ pub trait Itertools : Iterator {
         adaptors::dedup_by(self, cmp)
     }
 
+    /// Remove duplicates from sections of consecutive identical elements, while keeping a count of
+    /// how many repeated elements were present.
+    /// If the iterator is sorted, all elements will be unique.
+    ///
+    /// Iterator element type is `(usize, Self::Item)`.
+    ///
+    /// This iterator is *fused*.
+    ///
+    /// ```
+    /// use itertools::Itertools;
+    ///
+    /// let data = vec![1., 1., 2., 3., 3., 2., 2.];
+    /// itertools::assert_equal(data.into_iter().dedup_with_count(),
+    ///                         vec![(2, 1.), (1, 2.), (2, 3.), (2, 2.)]);
+    /// ```
+    fn dedup_with_count(self) -> DedupWithCount<Self>
+        where Self: Sized,
+    {
+        adaptors::dedup_with_count(self)
+    }
+
+    /// Remove duplicates from sections of consecutive identical elements, while keeping a count of
+    /// how many repeated elements were present.
+    /// This will determine equality using a comparison function.
+    /// If the iterator is sorted, all elements will be unique.
+    ///
+    /// Iterator element type is `(usize, Self::Item)`.
+    ///
+    /// This iterator is *fused*.
+    ///
+    /// ```
+    /// use itertools::Itertools;
+    ///
+    /// let data = vec![(0, 1.), (1, 1.), (0, 2.), (0, 3.), (1, 3.), (1, 2.), (2, 2.)];
+    /// itertools::assert_equal(data.into_iter().dedup_by_with_count(|x, y| x.1 == y.1),
+    ///                         vec![(2, (0, 1.)), (1, (0, 2.)), (2, (0, 3.)), (2, (1, 2.))]);
+    /// ```
+    fn dedup_by_with_count<Cmp>(self, cmp: Cmp) -> DedupByWithCount<Self, Cmp>
+        where Self: Sized,
+              Cmp: FnMut(&Self::Item, &Self::Item) -> bool,
+    {
+        adaptors::dedup_by_with_count(self, cmp)
+    }
+
     /// Return an iterator adaptor that filters out elements that have
     /// already been produced once during the iteration. Duplicates
     /// are detected using hash and equality.

tests/test_std.rs

@@ -114,6 +114,33 @@ fn dedup_by() {
     assert_eq!(&xs_d, &ys);
 }
 
+#[test]
+fn dedup_with_count() {
+    let xs: [i32; 8] = [0, 1, 1, 1, 2, 1, 3, 3];
+    let ys: [(usize, &i32); 5] = [(1, &0), (3, &1), (1, &2), (1, &1), (2, &3)];
+
+    it::assert_equal(ys.iter().cloned(), xs.iter().dedup_with_count());
+
+    let xs: [i32; 5] = [0, 0, 0, 0, 0];
+    let ys: [(usize, &i32); 1] = [(5, &0)];
+
+    it::assert_equal(ys.iter().cloned(), xs.iter().dedup_with_count());
+}
+
+
+#[test]
+fn dedup_by_with_count() {
+    let xs = [(0, 0), (0, 1), (1, 1), (2, 1), (0, 2), (3, 1), (0, 3), (1, 3)];
+    let ys = [(1, &(0, 0)), (3, &(0, 1)), (1, &(0, 2)), (1, &(3, 1)), (2, &(0, 3))];
+
+    it::assert_equal(ys.iter().cloned(), xs.iter().dedup_by_with_count(|x, y| x.1==y.1));
+
+    let xs = [(0, 1), (0, 2), (0, 3), (0, 4), (0, 5)];
+    let ys = [( 5, &(0, 1))];
+
+    it::assert_equal(ys.iter().cloned(), xs.iter().dedup_by_with_count(|x, y| x.0==y.0));
+}
+
 #[test]
 fn all_equal() {
     assert!("".chars().all_equal());