Q:

How do I calculate a value based on items in a filtered angularjs repeater

I'm building a scoring system and am trying to calculate a score based on values in a separate collection. I've been using this example: Calculating sum of repeated elements in AngularJS ng-repeat , but haven't been able to get it to work as I believe they're using one collection and not two. 
Here is my template using the suggestions from the question above:
<div>{{parent.id}}</div>
<div>{{ getTotal() }}</div>
<div ng-repeat="child in children | orderBy: '-postedTime' | filter: {parentId: parent.id}">
  <div>{{child.score}}</div>
</div>

The js:
$scope.getTotal = function(){
var total = 0;
for(var i = 0; i < $scope.children.length; i++){
    var score = $scope.child.score[i];
    total += (child.score);
}
return total;
}

Is there a way to sum all the scores from the filtered children and display on the parent?

A:

You can take the filter response  

ng-repeat="child in children | filter: {parentId: parent.id} as kids"

using as syntax in your children filter and use it in a sum filter which will display the sum of the scores of all children for a parent.

var app = angular.module('plunker', []);

angular.module('plunker')
  .controller('MainCtrl', function($scope) {


    $scope.totalScore = 0;

    $scope.parents = [{
      id: 1
    }, {
      id: 2
    }]

    $scope.children = [{
      parentId: 1,
      score: 25
    }, {
      parentId: 1,
      score: 25
    }, {
      parentId: 1,
      score: 25
    }, {
      parentId: 2,
      score: 25
    }];

  })


app.filter('sum', function() {
  return function(kids) {
    var total = 0;
    if (kids) {
      for (i = 0; i < kids.length; i++) {
        total = total + kids[i].score;
      };
    }
    return total;
  };
});
<!DOCTYPE html>
<html ng-app="plunker">

<head>
  <meta charset="utf-8" />
  <title>AngularJS Plunker</title>
  <link data-require="bootstrap-css@3.3.6" data-semver="3.3.6" rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.6/css/bootstrap.css" />
  <script>
    document.write('<base href="' + document.location + '" />');
  </script>
  <link rel="stylesheet" href="style.css" />
  <script data-require="angular.js@1.4.x" src="https://code.angularjs.org/1.4.9/angular.js" data-semver="1.4.9"></script>
  <script data-require="ui-bootstrap@*" data-semver="1.3.2" src="https://cdn.rawgit.com/angular-ui/bootstrap/gh-pages/ui-bootstrap-tpls-1.3.2.js"></script>
  <script src="app.js"></script>
  <script src="accounts.js"></script>
  <script src="controller.js"></script>
</head>

<body ng-controller="MainCtrl">
  <div ng-repeat="parent in parents">
    <div>parent id : {{parent.id}}</div>
    <div>total child scores : {{ kids | sum }}</div>
    <div ng-repeat="child in children | filter: {parentId: parent.id} as kids">
      <div>child Scores : {{child.score}}</div>
    </div>
  </div>


</body>

</html>

P.S : i did not have the exact JSON for parents and children so i have removed postedTime in children but you can use it in your actual code.

