Add a couple new collection methods from Ruby 2.0.

site/src/pages/enumerable.haml

@@ -124,6 +124,23 @@
   new Collection(0, false, null).any();
   // -> false</pre>
 
+  h3. @chunk(block, context)@
+
+  Splits the collection into groups of adjacent elements that return the same
+  value for the block, and returns an array whose elements contain the current
+  block value and the string of items that returned that value.
+
+  <pre>var list = new Collection([3, 1, 4, 1, 5, 9, 2, 6, 5, 3, 5]);
+  list.chunk(function(value) { return value % 2 === 0 })
+
+  // -> [
+  //        [false, [3, 1]],
+  //        [true,  [4]],
+  //        [false, [1, 5, 9]],
+  //        [true,  [2, 6]],
+  //        [false, [5, 3, 5]]
+  //    ]
+
   h3. @collect(block, context)@
 
   Alias for @map()@.

site/src/pages/hash.haml

@@ -281,6 +281,18 @@
 
   Returns @true@ iff the hash contains no data.
 
+  h3. @keepIf(predicate, context)@
+
+  Deletes all the pairs that do not satisfy the @predicate@ from the hash.
+  @context@ sets the binding of @this@ within the predicate function. For
+  example:
+
+  <pre>// Remove pairs for California and Illinois
+  senators.keepIf(function(pair) { return pair.key.code < 'M' });
+
+  // senators is now:
+  // { CA => feinstein, IL => burris }</pre>
+
   h3. @key(value)@
 
   Returns the first key from the hash whose corresponding value is @value@.

site/src/pages/set.haml

@@ -184,6 +184,17 @@
   Returns @true@ iff the receiver is a superset of the set @other@, that is if
   all the members of @other@ are also members of the receiver.
 
+  h3. @keepIf(predicate, context)@
+
+  Removes all the members of the set for which @predicate@ returns @false@.
+
+  <pre>var s = new Set([1,2,3,4,5,6,7,8,9]);
+
+  // Keep multiples of 3
+  s.keepIf(function(x) { return x % 3 == 0 });
+
+  // s == Set{3,6,9}</pre>
+
   h3. @merge(set)@
 
   Adds all the members of @set@ to the receiver.

source/enumerable.js

@@ -114,6 +114,29 @@ var Enumerable = new JS.Module('Enumerable', {
     return !!truth;
   },
 
+  chunk: function(block, context) {
+    if (!block) return this.enumFor('chunk');
+
+    var result  = [],
+        value   = null,
+        started = false;
+
+    this.forEach(function(item) {
+      var v = block.apply(context, arguments);
+      if (started) {
+        if (Enumerable.areEqual(value, v))
+          result[result.length - 1][1].push(item);
+        else
+          result.push([v, [item]]);
+      } else {
+        result.push([v, [item]]);
+        started = true;
+      }
+      value = v;
+    });
+    return result;
+  },
+
   count: function(block, context) {
     if (typeof this.size === 'function') return this.size();
     var count = 0, object = block;
@@ -494,6 +517,7 @@ Enumerable.alias({
   every:      'all',
   findAll:    'select',
   filter:     'select',
+  reduce:     'inject',
   some:       'any'
 });
 
@@ -548,8 +572,8 @@ Enumerable.extend({
       this._args   = (args || []).slice();
     },
 
-    // this is largely here to support testing
-    // since I don't want to make the ivars public
+    // this is largely here to support testing since I don't want to make the
+    // ivars public
     equals: function(enumerator) {
       return JS.isType(enumerator, this.klass) &&
              this._object === enumerator._object &&

source/hash.js

@@ -239,6 +239,12 @@ var Hash = new JS.Class('Hash', {
     return true;
   },
 
+  keepIf: function(block, context) {
+    return this.removeIf(function() {
+      return !block.apply(context, arguments);
+    });
+  },
+
   key: function(value) {
     var result = null;
     this.forEach(function(pair) {

source/set.js

@@ -162,6 +162,12 @@ var Set = new JS.Class('Set', {
     return other.isSubset(this);
   },
 
+  keepIf: function(block, context) {
+    return this.removeIf(function() {
+      return !block.apply(context, arguments);
+    });
+  },
+
   merge: function(list) {
     this.klass.forEach(list, function(item) { this.add(item) }, this);
   },

test/specs/enumerable_spec.js

@@ -124,6 +124,17 @@ JS.ENV.EnumerableSpec = JS.Test.describe(Enumerable, function() { with(this) {
     }})
   }})
 
+  describe("#chunk", function() { with(this) {
+    before(function() { with(this) {
+      this.items = list(3, 1, 4, 1, 5, 9, 2, 6, 5, 3, 5)
+    }})
+
+    it("groups the collection based on changes in the block's return value", function() { with(this) {
+      assertEqual( [ [false, [3,1]], [true, [4]], [false, [1,5,9,]], [true, [2,6]], [false, [5,3,5]] ],
+                   items.chunk(function(n) { return n % 2 === 0 }) )
+    }})
+  }})
+
   describe("#count", function() { with(this) {
     before(function() { with(this) {
       this.items = list(4,8,2,4,7)