From cc88a2d26c4e5ba60728d5d43743279f5c135a5e Mon Sep 17 00:00:00 2001
From: JarredAllen <jarredallen73@gmail.com>
Date: Tue, 11 Aug 2020 22:33:08 -0700
Subject: [PATCH 1/2] Create counts method and tests for it

---
 src/lib.rs        | 24 ++++++++++++++++++++++++
 tests/test_std.rs | 13 +++++++++++++
 2 files changed, 37 insertions(+)

diff --git a/src/lib.rs b/src/lib.rs
index eeecb1bb0..1412930b1 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -2807,6 +2807,30 @@ pub trait Itertools : Iterator {
     {
         multipeek_impl::multipeek(self)
     }
+
+    /// Collect the items in this iterator and return a `HashMap` which
+    /// contains each item that appears in the iterator and the number
+    /// of times it appears.
+    ///
+    /// # Examples
+    /// ```
+    /// # use itertools::Itertools;
+    /// let counts = [1, 1, 1, 3, 3, 5].into_iter().counts();
+    /// assert_eq!(counts[&1], 3);
+    /// assert_eq!(counts[&3], 2);
+    /// assert_eq!(counts[&5], 1);
+    /// assert_eq!(counts.get(&0), None);
+    /// ```
+    #[cfg(feature = "use_std")]
+    fn counts(self) -> HashMap<Self::Item, usize>
+    where
+        Self: Sized,
+        Self::Item: Eq + Hash,
+    {
+        let mut counts = HashMap::new();
+        self.for_each(|item| *counts.entry(item).or_default() += 1);
+        counts
+    }
 }
 
 impl<T: ?Sized> Itertools for T where T: Iterator { }
diff --git a/tests/test_std.rs b/tests/test_std.rs
index 9918592cb..0b28541f3 100644
--- a/tests/test_std.rs
+++ b/tests/test_std.rs
@@ -913,3 +913,16 @@ fn tree_fold1() {
         assert_eq!(actual, expected);
     }
 }
+
+#[test]
+fn counts() {
+    let a: [usize; 0] = [];
+    assert_eq!(0, a.iter().counts().len());
+    let b = [1, 1, 1, 2, 2, 3];
+    let b_counts = b.iter().counts();
+    assert_eq!(3, b_counts.len());
+    assert_eq!(Some(&3), b_counts.get(&1));
+    assert_eq!(Some(&2), b_counts.get(&2));
+    assert_eq!(Some(&1), b_counts.get(&3));
+    assert_eq!(None, b_counts.get(&4));
+}

From 1d05c2bb00d2bd118850baa227022ccb95d26f1b Mon Sep 17 00:00:00 2001
From: JarredAllen <jarredallen73@gmail.com>
Date: Tue, 18 Aug 2020 09:01:51 -0700
Subject: [PATCH 2/2] Change test to quickcheck

---
 tests/quick.rs    | 21 +++++++++++++++++++++
 tests/test_std.rs | 13 -------------
 2 files changed, 21 insertions(+), 13 deletions(-)

diff --git a/tests/quick.rs b/tests/quick.rs
index d509c7929..8208a887c 100644
--- a/tests/quick.rs
+++ b/tests/quick.rs
@@ -1188,3 +1188,24 @@ quickcheck! {
         }
     }
 }
+
+quickcheck! {
+    #[test]
+    fn counts(nums: Vec<isize>) -> TestResult {
+        let counts = nums.iter().counts();
+        for (&item, &count) in counts.iter() {
+            if count <= 0 {
+                return TestResult::failed();
+            }
+            if count != nums.iter().filter(|&x| x == item).count() {
+                return TestResult::failed();
+            }
+        }
+        for item in nums.iter() {
+            if !counts.contains_key(item) {
+                return TestResult::failed();
+            }
+        }
+        TestResult::passed()
+    }
+}
diff --git a/tests/test_std.rs b/tests/test_std.rs
index 0b28541f3..9918592cb 100644
--- a/tests/test_std.rs
+++ b/tests/test_std.rs
@@ -913,16 +913,3 @@ fn tree_fold1() {
         assert_eq!(actual, expected);
     }
 }
-
-#[test]
-fn counts() {
-    let a: [usize; 0] = [];
-    assert_eq!(0, a.iter().counts().len());
-    let b = [1, 1, 1, 2, 2, 3];
-    let b_counts = b.iter().counts();
-    assert_eq!(3, b_counts.len());
-    assert_eq!(Some(&3), b_counts.get(&1));
-    assert_eq!(Some(&2), b_counts.get(&2));
-    assert_eq!(Some(&1), b_counts.get(&3));
-    assert_eq!(None, b_counts.get(&4));
-}