ng-repeat with title and also sorting array

We have a JSON object and we do have a different requirement to display in a different form.

The object:

[
    {name: a1, marks:10},
    {name: b3, marks:10},
    {name: b2, marks:10},
    {name: c1, marks:10},
    {name: b1, marks:10},
    {name: a2, marks:10}
]

To display UI:

On click of sort by name

A: name: a1, name: a2, name: a3
B: name: b1, name: b2, name: b3
C: name: c1, name: c2, name: c3

And onclik of sort by marks (not to sort by name inside marks)

10: name: a2, name: c1, name: a3
11: name: a1, name: b2, name: b3
12: name: c1, name: a2, name: c3

Can anyone help please?

Have tried:

<div ng-repeat="letter in ['A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z']">
  <div class="folders_only col-xs-12"  ng-show="getFilesOfType(letter).length">
    <div>
      <span>{{letter}}</span>
    </div>
    <div ng-repeat='val in getFilesOfType(letter)'></div> 
  </div>
</div>

But problem is I have json object which gets more data on scrolling down each time, so new data doesnt reflect in UI