added an _.zip()

underscore.js

@@ -28,35 +28,10 @@ window._ = {
     return obj;
   },
   
-  // Determine whether all of the elements match a truth test. Delegate to
-  // Javascript 1.6's every(), if it is present.
-  all : function(obj, iterator, context) {
-    iterator = iterator || function(v){ return v; };
-    if (obj.every) return obj.every(iterator, context);
-    var result = true;
-    _.each(obj, function(value, index) {
-      result = result && !!iterator.call(context, value, index);
-      if (!result) throw '__break__';
-    });
-    return result;
-  },
-  
-  // Determine if at least one element in the object matches a truth test. Use
-  // Javascript 1.6's some(), if it exists.
-  any : function(obj, iterator, context) {
-    iterator = iterator || function(v) { return v; };
-    if (obj.some) return obj.some(iterator, context);
-    var result = false;
-    _.each(obj, function(value, index) {
-      if (result = !!iterator.call(context, value, index)) throw '__break__';
-    });
-    return result;
-  },
-  
   // Return the results of applying the iterator to each element. Use Javascript
   // 1.6's version of map, if possible.
   map : function(obj, iterator, context) {
-    if (obj.map) return obj.map(iterator, context);
+    if (obj && obj.map) return obj.map(iterator, context);
     var results = [];
     _.each(obj, function(value, index) {
       results.push(iterator.call(context, value, index));
@@ -64,7 +39,8 @@ window._ = {
     return results;
   },
   
-  // Aka reduce. Inject builds up a single result from a list of values.
+  // Inject builds up a single result from a list of values. Also known as
+  // reduce, and foldl.
   inject : function(obj, memo, iterator, context) {
     _.each(obj, function(value, index) {
       memo = iterator.call(context, memo, value, index);
@@ -104,6 +80,31 @@ window._ = {
     return results;
   },
   
+  // Determine whether all of the elements match a truth test. Delegate to
+  // Javascript 1.6's every(), if it is present.
+  all : function(obj, iterator, context) {
+    iterator = iterator || function(v){ return v; };
+    if (obj.every) return obj.every(iterator, context);
+    var result = true;
+    _.each(obj, function(value, index) {
+      result = result && !!iterator.call(context, value, index);
+      if (!result) throw '__break__';
+    });
+    return result;
+  },
+  
+  // Determine if at least one element in the object matches a truth test. Use
+  // Javascript 1.6's some(), if it exists.
+  any : function(obj, iterator, context) {
+    iterator = iterator || function(v) { return v; };
+    if (obj.some) return obj.some(iterator, context);
+    var result = false;
+    _.each(obj, function(value, index) {
+      if (result = !!iterator.call(context, value, index)) throw '__break__';
+    });
+    return result;
+  },
+  
   // Determine if a given value is included in the array or object, 
   // based on '=='.
   include : function(obj, target) {
@@ -239,6 +240,16 @@ window._ = {
     });
   },
   
+  // Zip together multiple lists into a single array -- elements that share
+  // an index go together.
+  zip : function() {
+    var args = _.toArray(arguments);
+    var length = _.max(_.pluck(args, 'length'));
+    var results = new Array(length);
+    for (var i=0; i<length; i++) results[i] = _.pluck(args, String(i));
+    return results;
+  },
+  
   // If the browser doesn't supply us with indexOf (I'm looking at you, MSIE), 
   // we need this function. Return the position of the first occurence of an 
   // item in an array, or -1 if the item is not included in the array.
@@ -252,7 +263,7 @@ window._ = {
   /* -------------- The following methods apply to functions -----------------*/
   
   // Create a function bound to a given object (assigning 'this', and arguments,
-  // optionally).
+  // optionally). Binding with arguments is also known as 'curry'.
   bind : function(func, context) {
     if (!context) return func;
     var args = _.toArray(arguments).slice(2);