diff --git a/utils-tests.rkt b/utils-tests.rkt
index 89189aa..bb6eafe 100644
--- a/utils-tests.rkt
+++ b/utils-tests.rkt
@@ -113,8 +113,10 @@
 
 (test-case "Additional list utilties"
   (let-values ([(e1 l1) (collect-by-key '((1 2) (1 3)) '(a b))]
-               [(e2 l2) (collect-by-key '((1 2) (1 2)) '(a b))])
+               [(e2 l2) (collect-by-key '((1 2) (1 2)) '(a b))]
+               [(e3 l3) (collect-by-key/sets '(a b a) '(1 2 1))])
     (check-equal? e1 '((1 2) (1 3))) (check-equal? l1 '((a) (b)))
-    (check-equal? e2 '((1 2))) (check-equal? l2 '((b a))))
+    (check-equal? e2 '((1 2))) (check-equal? l2 '((b a)))
+    (check-equal? e3 '(a b)) (check-equal? l3 (list (set 1) (set 2))))
   (check-equal? (ht-values:list->set #hash((a . (1 1))))
                 (hash 'a (set 1))))
diff --git a/utils.rkt b/utils.rkt
index 56459df..e29c6e7 100644
--- a/utils.rkt
+++ b/utils.rkt
@@ -26,6 +26,7 @@
                                   graph?)]
                [pretty-print-set (-> generic-set? string?)]
                [collect-by-key (-> (listof any/c) (listof any/c) (values (listof any/c) (listof any/c)))]
+               [collect-by-key/sets (-> (listof any/c) (listof any/c) (values (listof any/c) (listof (set/c any/c))))]
 
                [ht-values:list->set (-> (hash/c any/c (listof any/c)) (hash/c any/c (set/c any/c)))])
  ;; Contracts
@@ -280,6 +281,11 @@
             ([e edges] [l labels])
     (hash-update ht e (λ (ls) (cons l ls)) empty)))
 
+;;; Like collect-by-key, but returns a list of sets of weights.
+(define (collect-by-key/sets edges labels)
+  (let-values ([(es ls) (collect-by-key edges labels)])
+    (values es (map list->set ls))))
+
 ;;; Converts the values of a hash table from lists to sets.
 (define (ht-values:list->set ht)
   (for/hash ([(k v) (in-hash ht)])