grouping items in an Ember.ArrayController

line_items.handlebars

    <table>
      {{#each category in categories}}
        <thead>
          <tr>
            <th class="large">
              {{category.name}}
            </th>
          </tr>
          <tr>
            <th>Line Item</th>
          </tr>
        </thead>
        <tbody>
          {{#each line_item in category.line_items}}
            {{ render "line_item" line_item }}
          {{/each}}
        </tbody>
      {{/each}}
    </table>

line_items_controller.js.coffee

App.LineItemsController = Ember.ArrayController.extend
  categories: (->
    @get('model').mapBy('category').uniq().map (category) =>
      Ember.Object.create
        name: category
        line_items: @get('model').filterBy 'category', category
  ).property('@each.category')