[
  {
    category: 'alpha',
    id: 3,
    group: 'a'
  },{
    category: 'beta',
    id: 2,
    group: 'a'
  }, {
    category: 'gamma',
    id: 1,
    group: 'b'
  }
]

ng-repeat="(i, category) in array | orderBy: 'id' | groupBy: 'group' "
    {{ i }}
    ng-repeta="item in category" 
    {{ item.category }}