1 files changed, 14 insertions, 4 deletions
diff --git a/src/group_map.rs b/src/group_map.rs
index be9f842..4231de0 100644
--- a/src/group_map.rs
+++ b/src/group_map.rs
@@ -14,9 +14,19 @@ pub fn into_group_map<I, K, V>(iter: I) -> HashMap<K, Vec<V>>
 {
     let mut lookup = HashMap::new();
 
-    for (key, val) in iter {
-        lookup.entry(key).or_insert(Vec::new()).push(val);
-    }
+    iter.for_each(|(key, val)| {
+        lookup.entry(key).or_insert_with(Vec::new).push(val);
+    });
 
     lookup
-}
-\ No newline at end of file
+}
+
+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))
+    )
+}