Merge upstream

Author: SkiFire13

src/group_map.rs

@@ -19,4 +19,16 @@ pub fn into_group_map<I, K, V>(iter: I) -> HashMap<K, Vec<V>>
     }
 
     lookup
-}
+}
+
+pub fn into_group_map_by<I, K, V>(iter: I, f: impl Fn(&V) -> K) -> HashMap<K, Vec<V>>
+    where
+        I: Iterator<Item=V>,
+        K: Hash + Eq,
+{
+    into_group_map(
+        iter.map(|v| (f(&v), v))
+    )
+}
+
+

src/lib.rs

@@ -2332,6 +2332,41 @@ pub trait Itertools : Iterator {
         group_map::into_group_map(self)
     }
 
+    /// Return an `Iterator` on a HahMap. Keys mapped to `Vec`s of values. The key is specified in
+    /// in the closure.
+    /// Different of into_group_map_by because the key is still present. It is also more general.
+    /// you can also fold the group_map.
+    ///
+    /// ```
+    /// use itertools::Itertools;
+    /// use std::collections::HashMap;
+    ///
+    /// let data = vec![(0, 10), (2, 12), (3, 13), (0, 20), (3, 33), (2, 42)];
+    /// let lookup: HashMap<u32,Vec<(u32, u32)>> = data.clone().into_iter().into_group_map_by(|a|
+    /// a.0);
+    ///
+    /// assert_eq!(lookup[&0], vec![(0,10),(0,20)]);
+    /// assert_eq!(lookup.get(&1), None);
+    /// assert_eq!(lookup[&2], vec![(2,12), (2,42)]);
+    /// assert_eq!(lookup[&3], vec![(3,13), (3,33)]);
+    ///
+    /// assert_eq!(
+    ///     data.into_iter()
+    ///     .into_group_map_by(|x| x.0)
+    ///     .into_iter()
+    ///     .map(|(key, values)| (key, values.into_iter().fold(0,|acc, (_,v)| acc + v )))
+    ///     .collect::<HashMap<u32,u32>>()[&0], 30)
+    /// ```
+    #[cfg(feature = "use_std")]
+    fn into_group_map_by<K, V, F>(self, f: F) -> HashMap<K, Vec<V>>
+        where
+            Self: Iterator<Item=V> + Sized,
+            K: Hash + Eq,
+            F: Fn(&V) -> K,
+    {
+        group_map::into_group_map_by(self, f)
+    }
+
     /// Constructs a `GroupingMap` to be used later with one of the efficient 
     /// group-and-fold operations it allows to perform.
     /// 

src/sources.rs

@@ -76,22 +76,21 @@ impl<A, F> Iterator for RepeatCall<F>
 ///
 /// use itertools::unfold;
 ///
-/// let (mut x1, mut x2) = (1u32, 1u32);
-/// let mut fibonacci = unfold((), move |_| {
+/// let mut fibonacci = unfold((1u32, 1u32), |(x1, x2)| {
 ///     // Attempt to get the next Fibonacci number
-///     let next = x1.saturating_add(x2);
+///     let next = x1.saturating_add(*x2);
 ///
 ///     // Shift left: ret <- x1 <- x2 <- next
-///     let ret = x1;
-///     x1 = x2;
-///     x2 = next;
+///     let ret = *x1;
+///     *x1 = *x2;
+///     *x2 = next;
 ///
 ///     // If addition has saturated at the maximum, we are finished
-///     if ret == x1 && ret > 1 {
-///         return None;
+///     if ret == *x1 && ret > 1 {
+///         None
+///     } else {
+///         Some(ret)
 ///     }
-///
-///     Some(ret)
 /// });
 ///
 /// itertools::assert_equal(fibonacci.by_ref().take(8),