Category talk:Wren-seq: Difference between revisions

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@@ Line 202: / Line 202: @@
         }
         return g
+    }
+    // Applies a function to each element of a list to produce a key and returns a map of each
+    // distinct key to a list of the corresponding elements. The latter retain their original
+    // order within the list and the key must be a value type.
+    static groupBy(a, fn) {
+        isList_(a)
+        var m = {}
+        for (e in a) {
+            var k = fn.call(e)
+            if (!m.containsKey(k)) {
+                m[k] = [e]
+            } else {
+                m[k].add(e)
+            }
+        }
+        return m
     }