From 1a9518ec04503b82830445eccafd71aadb8c0dbd Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Hugo=20H=C3=B6rnquist?= <hugo@lysator.liu.se>
Date: Wed, 1 Apr 2020 20:59:45 +0200
Subject: Add group-by.

---
 module/util.scm | 6 ++++++
 1 file changed, 6 insertions(+)

(limited to 'module')

diff --git a/module/util.scm b/module/util.scm
index 8ccfa27e..d4c318a3 100644
--- a/module/util.scm
+++ b/module/util.scm
@@ -398,6 +398,12 @@
             (assq-set! alist k (append v (or o '())))))
         (copy-tree a) b))
 
+(define-public (group-by proc lst)
+  (let ((h (make-hash-table)))
+    (for value in lst
+         (let ((key (proc value)))
+           (hash-set! h key (cons value (hash-ref h key '())))))
+    (hash-map->list list h)))
 
 (define-macro (use-modules* . forms)
   `(use-modules
-- 
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