Add all_equal

Author: philipp

src/lib.rs

@@ -732,6 +732,29 @@ pub trait Itertools : Iterator {
         adaptors::unique(self)
     }
 
+    /// Check whether all elements compare equal.
+    ///
+    /// Empty iterators are considered to have equal elements:
+    ///
+    /// ```
+    /// use itertools::Itertools;
+    ///
+    /// let data = vec![1, 1, 1, 2, 2, 3, 3, 3, 4, 5, 5];
+    /// assert!(!data.iter().all_equal());
+    /// assert!(data[0..3].iter().all_equal());
+    /// assert!(data[3..5].iter().all_equal());
+    /// assert!(data[5..8].iter().all_equal());
+    ///
+    /// let data : Option<usize> = None;
+    /// assert!(data.into_iter().all_equal());
+    /// ```
+    fn all_equal(self) -> bool 
+        where Self: Sized,
+              Self::Item: PartialEq,
+    {
+        self.dedup().nth(1).is_none()
+    }
+
     /// Return an iterator adaptor that filters out elements that have
     /// already been produced once during the iteration.
     ///

tests/tests.rs

@@ -185,6 +185,15 @@ fn dedup() {
     assert_eq!(&xs_d, &ys);
 }
 
+#[test]
+fn all_equal() {
+    assert!(!"AABBCCC".chars().all_equal());
+    assert!("AAAAAAA".chars().all_equal());
+    for (_key, sub) in &"AABBCCC".chars().group_by(|&x| x) {
+        assert!(sub.all_equal());
+    }
+}
+
 #[test]
 fn unique_by() {
     let xs = ["aaa", "bbbbb", "aa", "ccc", "bbbb", "aaaaa", "cccc"];