Add init(), tail() and reverse() Array functions. Alias first() to head();

test/arrays.js

@@ -58,4 +58,19 @@ $(document).ready(function() {
     equals(_.lastIndexOf(numbers, 0), 8, 'lastIndexOf the other element');
   });
   
+  test("arrays: tail", function() {
+    var numbers = [1, 2, 3, 4];
+    equals(_.tail(numbers).join(", "), "2, 3, 4");
+  });
+  
+  test("arrays: init", function() {
+    var numbers = [1, 2, 3, 4];
+    equals(_.init(numbers).join(", "), "1, 2, 3");
+  });
+  
+  test("arrays: reverse", function() {
+    var numbers = [1, 2, 4, 6];
+    equals(_.reverse(numbers).join(", "), "6, 4, 2, 1");
+  });
+  
 });

underscore.js

@@ -305,6 +305,29 @@
     while (i--) if (array[i] === item) return i;
     return -1;
   };
+  
+  // Returns everything but the first entry of the array. Conceptually the 
+  // same as calling shift(), but doesn't mutate the array passed in.
+  _.tail = function(array) {
+    var tail = _.clone(array);
+    tail.shift();
+    return tail;
+  };
+  
+  // Returns everything but the last entry of the array. Conceptually the 
+  // same as calling pop(), but doesn't mutate the array passed in.
+  _.init = function(array) {
+    var init = _.clone(array);
+    init.pop();
+    return init;
+  };
+
+  // Returns a new array, with the entries or the passed-in array in reverse
+  // order.
+  _.reverse = function(array) {
+    var reverse = _.clone(array);
+    return reverse.reverse();
+  };
 
   /* ----------------------- Function Functions: -----------------------------*/
 
@@ -501,6 +524,7 @@
 
   /*------------------------------- Aliases ----------------------------------*/
 
+  _.head     = _.first;
   _.forEach  = _.each;
   _.foldl    = _.inject       = _.reduce;
   _.foldr    = _.reduceRight;