jQuery: sortable portfolio

HTML

<div id="top">
 &nbsp;
</div>
<div id="portfolio">
    <div id="portfolio-sort">
        <a href="#" id="all">ALL</a>
        <a href="#" data-cat="a">A</a>
        <a href="#" data-cat="b">B</a>
        <a href="#" data-cat="c">C</a>
    </div>
    <div id="sortable">
        <div class="folio-item" data-cat="a">A</div>
        <div class="folio-item" data-cat="b">B</div>
        <div class="folio-item" data-cat="c">C</div>
        <div class="folio-item" data-cat="c">C</div>
        <div class="folio-item" data-cat="b">B</div>
        <div class="folio-item" data-cat="a">A</div>
        <div class="folio-item" data-cat="a">A</div>
        <div class="folio-item" data-cat="c">C</div>
        <div class="folio-item" data-cat="b">B</div>
    </div>
</div>
<div id="bottom">
&nbsp;
</div>

CSS

#top {
  background-color:#ccc;
  height:600px;
}
#bottom {
  background-color:#ddd;
  height: 400px;
}
#portfolio {
    width: 100%;
    max-width: 600px;
    margin: 2em auto;
}

#portfolio-sort {
    text-align: center;
    padding-bottom: 3px;
    border-bottom: 1px solid #999;
    margin-bottom: 1em;
}

#portfolio-sort a {
    color: #fff;
    background: #a00;
    display: inline-block;
    padding: 3px 9px;
    text-decoration: none;
    margin-right: 1em;
}

#sortable {
    overflow: hidden;
}

div.folio-item {
    float: left;
    margin: 0 3% 1em 0;
    width: 29%;
    height: 10em;
    line-height: 10;
    text-align: center;
}

div[data-cat="a"] {
    background: #ccc;
}

div[data-cat="b"] {
    background: #666;
    color: #fff;
}

div[data-cat="c"] {
    background: #333;
    color: #fff;
}

JavaScript

var Portfolio = {
    sort: function(items) {
        items.show();
        $('#sortable').find('div.folio-item').not(items).fadeOut(500);
    },
    showAll: function(items) {
        items.fadeIn(500);
    },
    doSort: function() {
        $('a', '#portfolio-sort').on('click', function() {

            var $a = $(this);
            if (!$a.is('#all')) {

                var items = $('div[data-cat=' + $a.data('cat') + ']', '#sortable');

                Portfolio.sort(items);

            } else {

                Portfolio.showAll($('div.folio-item', '#sortable'));


            }

        });
    }
};

Portfolio.doSort();