Tweaking _.sample to taste.

test/collections.js

@@ -467,7 +467,7 @@ $(document).ready(function() {
     strictEqual(_.sample([]), undefined, 'sampling empty array with no number returns undefined');
     notStrictEqual(_.sample([], 5), [], 'sampling empty array with a number returns an empty array');
     notStrictEqual(_.sample([1, 2, 3], 0), [], 'sampling an array with 0 picks returns an empty array');
-    throws(function() { _.sample([], -1); }, 'cannot sample a negative number of picks');
+    deepEqual(_.sample([1, 2], -1), [], 'sampling a negative number of picks returns an empty array');
   });
 
   test('toArray', function() {

underscore.js

@@ -283,19 +283,6 @@
     return result.value;
   };
 
-  // Sample a number of random values from an array.
-  // If number is not specified, returns only a single sampled object
-  // Otherwise, returns an array of (min of number and length of array) sampled objects
-  _.sample = function(obj, number) {
-    if (typeof number === 'number') {
-      if (number < 0) {
-        throw new Error('sample cannot be called with a negative number of picks');
-      }
-      return _.shuffle(obj).slice(0, number);
-    }
-    return obj[_.random(obj.length - 1)];
-  };
-
   // Shuffle an array.
   _.shuffle = function(obj) {
     var rand;
@@ -309,6 +296,16 @@
     return shuffled;
   };
 
+  // Sample **n** random values from an array.
+  // If **n** is not specified, returns a single random element from the array.
+  // The internal `guard` argument allows it to work with `map`.
+  _.sample = function(obj, n, guard) {
+    if (arguments.length < 2 || guard) {
+      return obj[_.random(obj.length - 1)];
+    }
+    return _.shuffle(obj).slice(0, Math.max(0, n));
+  };
+
   // An internal function to generate lookup iterators.
   var lookupIterator = function(value) {
     return _.isFunction(value) ? value : function(obj){ return obj[value]; };