another take at allowing for array of iteratees in sortBy

test/collections.js

@@ -496,6 +496,10 @@
 
     list = ['q', 'w', 'e', 'r', 't', 'y'];
     deepEqual(_.sortBy(list), ['e', 'q', 'r', 't', 'w', 'y'], 'uses _.identity if iterator is not specified');
+
+    var people2 = [{name : 'curly', age : 50},{name: 'moe', age: 30},{name : 'curly', age : 27}];
+    people2 = _.sortBy(people2, ['name',function(p){return p.age;}] );
+    deepEqual(_.pluck(people2, 'age'), [27,50,30], 'stooges sorted first by name, then age');
   });
 
   test('groupBy', function() {

underscore.js

@@ -334,21 +334,28 @@
     return _.shuffle(obj).slice(0, Math.max(0, n));
   };
 
-  // Sort the object's values by a criterion produced by an iteratee.
+  // Sort the object's values by a criterion produced by one or more iteratees.
   _.sortBy = function(obj, iteratee, context) {
-    iteratee = _.iteratee(iteratee, context);
+    var iteratees = [].concat(iteratee).map(function(i){
+      return _.iteratee(i,context);
+    });
+    var length = iteratees.length;
     return _.pluck(_.map(obj, function(value, index, list) {
       return {
         value: value,
         index: index,
-        criteria: iteratee(value, index, list)
+        criterias: _.map(iteratees,function(it){
+          return it(value,index,list);
+        })
       };
     }).sort(function(left, right) {
-      var a = left.criteria;
-      var b = right.criteria;
-      if (a !== b) {
-        if (a > b || a === void 0) return 1;
-        if (a < b || b === void 0) return -1;
+      for (var n = 0; n < length; n++) {
+        var a = left.criterias[n];
+        var b = right.criterias[n];
+        if (a !== b) {
+          if (a > b || a === void 0) return 1;
+          if (a < b || b === void 0) return -1;
+        }
       }
       return left.index - right.index;
     }), 'value');