Group and count HTML elements by data attribute in jQuery

I'm trying to group each instance of a data attribute into a list from the number of occurrences of each attribute in a page, using jQuery. Similar to grouping categories or tags in a news section.

For example, I would like to create something like this:

• Category 1 (5)
• Category 2 (3)
• Category 3 (1)

from this html:

<ul class="categories">
   <li data-category="category-1">Category 1</li>
   <li data-category="category-1">Category 1</li>
   <li data-category="category-1">Category 1</li>
   <li data-category="category-1">Category 1</li>
   <li data-category="category-1">Category 1</li>
   <li data-category="category-2">Category 2</li>
   <li data-category="category-2">Category 2</li>
   <li data-category="category-2">Category 2</li>
   <li data-category="category-3">Category 3</li>
</ul>

How can I achieve this in jQuery? Is it even possible?

It is possible, check this jsFiddle I've created.

var categories = {},
    category;

$('.categories li[data-category]').each(function(i, el){
    category = $(el).data('category');
    if (categories.hasOwnProperty(category)) {
        categories[category] += 1;
    }
    else {
        categories[category] = 1;
    }
});

// print results
for(var key in categories){
    console.log(key + ' (' + categories[key] + ')');
}