Add group by support to ngRepeat

[rzschech]

It would be nice if ngRepeat supported simple grouping similar to the select directive's option groups. For example:

<div ng-controller="MyCntrl">
  <div ng-repeat="(shade, shadeColors) in colors group by c.shade">
    <div>
      Shade: {{shade}}
      <div ng-repeat="color in shadeColors">
        Color: {{color.name}}
      </div>
    </div>
  </div>
</div>

function MyCntrl($scope) {
  $scope.colors = [
    {name:'black', shade:'dark'},
    {name:'white', shade:'light'},
    {name:'red', shade:'dark'},
    {name:'blue', shade:'dark'},
    {name:'yellow', shade:'light'}
  ];
}

Would produce the following:

<div>
  <div>
    <div>
      Shade: dark
      <div>
        Color: black
      </div>
      <div>
        Color: red
      </div>
      <div>
        Color: blue
      </div>
    </div>
    <div>
      Shade: light
      <div>
        Color: white
      </div>
      <div>
        Color: yellow
      </div>
    </div>
  </div>
</div>

[bhollis]

See http://stackoverflow.com/questions/16507040/angular-filter-works-but-causes-10-digest-iterations-reached (and many more similar StackOverflow posts) for examples of people trying to build their own grouping features and running into problems. A lot of people are using a naive _.memoize from Underscore, but that's just a memory leak.

It'd be great if we could get guidance from Angular experts as to the best way to do grouped repeats/filters, or if support could be added directly to the framework.

[quantizor]

+1 working on a similar problem here

[thorn0]

#1649 was closed with "this isn't hard to implement yourself if needed", but in fact it's really hard.