SegFaultAX · May 8, 2014 18:23 · May 8, 2014
diff --git a/gistfile1.txt b/gistfile1.txt
@@ -0,0 +1,14 @@
+def categorize(fn, coll):
+    """Like group_by, but fn returns multiple keys"""
+
+    acc = {}
+    for e in coll:
+        keys = fn(e)
+        for key in keys:
+            if key not in acc:
+                acc[key] = []
+            acc[key].append(e)
+    return acc
+
+def group_by(fn, l):
+    return categorize(lambda e: [fn(e)], l)