Are the sorting algorithms for BackboneJS and AngularJS considered stable sorting methods?

Question

Are the sorting algorithms for BackboneJS and AngularJS considered stable sorting methods?

I'm considering incorporating BackboneJS and AngularJS into my app. However, I'm curious about the stability of sorting algorithms in these frameworks. Specifically, I would like to know if they maintain the order of previously sorted columns within a table or collection.

angularjs algorithm sorting backbone.js

Answer 1

Answer №1

Regarding Angular, I'm not certain, but when it comes to Backbone, the stability of sorting may vary depending on how it is implemented.

The sorting of all collections in Backbone is handled by

Backbone.Collection.prototype.sort

. Upon inspecting this method in the source code here:

if (_.isString(this.comparator) || this.comparator.length === 1) {
  this.models = this.sortBy(this.comparator, this);
} else {
  this.models.sort(_.bind(this.comparator, this));
}

If the defined comparator for your collection is a string (like a model attribute name) or a function that takes only one argument, then the sorting is done using _.sortBy, as explained in _.sortBy.

This function returns a sorted copy of the list, with stability ensured...

Further investigations into the underlying implementation reveal that stability is maintained by utilizing the element index as a secondary sorting factor.

If the collection's comparator cannot be utilized with _.sortBy, then resorting is carried out using Array.prototype.sort, which does not ensure stability.

Answer 2

Regarding Angular, I'm not certain, but when it comes to Backbone, the stability of sorting may vary depending on how it is implemented.

The sorting of all collections in Backbone is handled by

Backbone.Collection.prototype.sort

. Upon inspecting this method in the source code here:

if (_.isString(this.comparator) || this.comparator.length === 1) {
  this.models = this.sortBy(this.comparator, this);
} else {
  this.models.sort(_.bind(this.comparator, this));
}

If the defined comparator for your collection is a string (like a model attribute name) or a function that takes only one argument, then the sorting is done using _.sortBy, as explained in _.sortBy.

This function returns a sorted copy of the list, with stability ensured...

Further investigations into the underlying implementation reveal that stability is maintained by utilizing the element index as a secondary sorting factor.

If the collection's comparator cannot be utilized with _.sortBy, then resorting is carried out using Array.prototype.sort, which does not ensure stability.

Answer 3

Answer №2

When using the orderBy filter in Angular (specifically v1.3), it sorts stably based on the original list rather than the current sorted list while using ng-repeat. This can result in unexpected outcomes, though it is not an unstable sort.

Consider a basic controller in an Angular app:

angular.module('myApp', [])
  .controller('SortingCtrl', function ($scope) {
    $scope.items = [
      {
        name: 'A',
        value1: 5,
        value2: 10,
        value3: 0
      }, {
        name: 'B',
        value1: 2,
        value2: 15,
        value3: 0
      }, {
        name: 'C',
        value1: 6,
        value2: 12,
        value3: 0
      }
    ];

    $scope.sort = {
      predicate: 'name'
    };

  });

Accompanied by a simple view:

<body ng-controller="SortingCtrl">

  <select ng-model="sort.predicate">
    <option>name</option>
    <option>value1</option>
    <option>value2</option>
    <option>value3</option>
  </select>

  <table>
    <tr>
      <th>name</th>
      <th>value1</th>
      <th>value2</th>
      <th>value3</th>
    </tr>
    <tr ng-repeat="item in items | orderBy:sort.predicate">
      <td>{{ item.name }}</td>
      <td>{{ item.value1 }}</td>
      <td>{{ item.value2 }}</td>
      <td>{{ item.value3 }}</td>
    </tr>
  </table>

</body>

If you initially sort by value1 or value2, the results will be as expected. However, if you then decide to sort by value3, with all values being 0, you might assume the table order remains the same. Surprisingly, it resorts to its original order A, B, C.

This behavior doesn't indicate that the orderBy filter in Angular isn't stable, but it may produce surprising outcomes. You can see this demonstrated in the following Plunker link: http://plnkr.co/edit/rwrMQXSsB9wU3KBnWZBk?p=preview

Answer 4

When using the orderBy filter in Angular (specifically v1.3), it sorts stably based on the original list rather than the current sorted list while using ng-repeat. This can result in unexpected outcomes, though it is not an unstable sort.

Consider a basic controller in an Angular app:

angular.module('myApp', [])
  .controller('SortingCtrl', function ($scope) {
    $scope.items = [
      {
        name: 'A',
        value1: 5,
        value2: 10,
        value3: 0
      }, {
        name: 'B',
        value1: 2,
        value2: 15,
        value3: 0
      }, {
        name: 'C',
        value1: 6,
        value2: 12,
        value3: 0
      }
    ];

    $scope.sort = {
      predicate: 'name'
    };

  });

Accompanied by a simple view:

<body ng-controller="SortingCtrl">

  <select ng-model="sort.predicate">
    <option>name</option>
    <option>value1</option>
    <option>value2</option>
    <option>value3</option>
  </select>

  <table>
    <tr>
      <th>name</th>
      <th>value1</th>
      <th>value2</th>
      <th>value3</th>
    </tr>
    <tr ng-repeat="item in items | orderBy:sort.predicate">
      <td>{{ item.name }}</td>
      <td>{{ item.value1 }}</td>
      <td>{{ item.value2 }}</td>
      <td>{{ item.value3 }}</td>
    </tr>
  </table>

</body>

If you initially sort by value1 or value2, the results will be as expected. However, if you then decide to sort by value3, with all values being 0, you might assume the table order remains the same. Surprisingly, it resorts to its original order A, B, C.

This behavior doesn't indicate that the orderBy filter in Angular isn't stable, but it may produce surprising outcomes. You can see this demonstrated in the following Plunker link: http://plnkr.co/edit/rwrMQXSsB9wU3KBnWZBk?p=preview

Are the sorting algorithms for BackboneJS and AngularJS considered stable sorting methods?

Answer №1

Answer №2

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