[javascript] jQuery Array of all selected checkboxes (by class)

Possible Duplicate:
Select values of checkbox group with jQuery

In HTML I have a set of checkboxes grouped together by a class. I want to get an array in jQuery containing all the checkboxes that are selected/checked for that class (so other checkboxes on the page are ignored).

So HTML code like this:

<input type="checkbox" class="group1" value="18" checked="checked" />
<input type="checkbox" class="group1" value="20" />
<input type="checkbox" class="group1" value="15" />
<input type="checkbox" class="group2" value="14" />
<input type="checkbox" class="group1" value="55" checked="checked" />
<input type="checkbox" class="group1" value="10" checked="checked" />
<input type="checkbox" class="group2" value="77" checked="checked" />
<input type="checkbox" class="group1" value="11" />

Would return the values of the checked/selected group1 checkboxes into an array like this:

var values = [ 18, 55, 10 ];

var matches = [];
$(".className:checked").each(function() {
    matches.push(this.value);
});

You can also add underscore.js to your project and will be able to do it in one line:

_.map($("input[name='category_ids[]']:checked"), function(el){return $(el).val()})