From 9a7d9e7bb844f49b694e017e2f96342386e3af63 Mon Sep 17 00:00:00 2001
From: John-David Dalton <john.david.dalton@gmail.com>
Date: Thu, 6 Sep 2012 22:35:20 -0700
Subject: [PATCH] Ensure `_.sortBy` is stable for `undefined` values.

Former-commit-id: bf250150d27de050ea7a6fa376aacdc8d1ba7716
---
 lodash.js    | 3 +++
 test/test.js | 5 ++++-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/lodash.js b/lodash.js
index a70063fed..c67cd23b1 100644
--- a/lodash.js
+++ b/lodash.js
@@ -757,6 +757,9 @@
     a = a.criteria;
     b = b.criteria;
 
+    if (a === b) {
+      return ai < bi ? -1 : 1;
+    }
     if (a === undefined) {
       return 1;
     }
diff --git a/test/test.js b/test/test.js
index f8243e949..99f2622a0 100644
--- a/test/test.js
+++ b/test/test.js
@@ -1340,7 +1340,10 @@
         new Pair(1, 5), new Pair(1, 6),
         new Pair(2, 1), new Pair(2, 2),
         new Pair(2, 3), new Pair(2, 4),
-        new Pair(2, 5), new Pair(2, 6)
+        new Pair(2, 5), new Pair(2, 6),
+        new Pair(undefined, 1), new Pair(undefined, 2),
+        new Pair(undefined, 3), new Pair(undefined, 4),
+        new Pair(undefined, 5), new Pair(undefined, 6)
       ];
 
       var actual = _.sortBy(collection, function(pair) {