ng-group

An Angular.js filter for grouping items in an array by one of their fields.

Usage

The package ng-group provides a filter named groupBy for use with ng-repeat.

Example

Say you have an array of objects representing people:

$scope.people = [
  {name: "Frodo Baggins", home: "The Shire"},
  {name: "Samwise Gamgee", home: "The Shire"},
  {name: "Aragorn", home: "Gondor"},
  {name: "Legolas", home: "Mirkwood"},
  /* ... */
];

and you want to display them arranged according to the place they call home:

The Shire

• Frodo Baggins
• Samwise Gamgee

Gondor

• Aragorn

Mirkwood

• Legolas

Applying the groupBy:'home' filter to people produces an array of places and the people who live there. You can loop through the places with ng-repeat, then loop through the people for a given place with another, nested ng-repeat, like this:

<div ng-repeat="placePeople in people | groupBy:'home':'peopleByHome'">
  <h3>{{placePeople.home}}</h3>
  <ul>
    <li ng-repeat="person in placePeople.items">{{person.name}}</li>
  </ul>
</div>

Angular's two-way data-binding will work as normal. If you remove an item from the array, it will be removed from the view; if it was the only item in its group, the group will be removed as well.

See a working, editable version of the above example on CodePen.

Installing

1. Add ngGroup.js to your app:

   • If you use Bower, just bower install ng-group.
   • otherwise, copy src/ngGroup.js into your app.

2. Load ngGroup.js via a script tag. N.B. it must be loaded after Angular.js, but before your app code.

   <script src="https://github.com/samstokes/ng-group/raw/master/path/to/angular.js"></script>
   <script src="https://github.com/samstokes/ng-group/raw/master/path/to/ngGroup.js"></script> <!-- add this -->
   <script src="https://github.com/samstokes/ng-group/raw/master/YourApp.js"></script>

3. Add the ng.group module to your app's dependencies:

   var app = angular.module('YourApp', [
       'ng.group'                             // add this
   ]);
   
   app.controller('YourCtrl', function () {
     // ...
   });

4. Now you can use the groupBy filter in your views:

   <div ng-repeat="placePeople in people | groupBy:'home':'peopleByHome'">
     <!-- ... -->
   </div>

Details

• Group field: The first argument to the filter is the name of the property to group by. It can be the name of an object property (e.g. person.home) or an object method (e.g. person.home()).

  N.B. this argument will be evaluated as an Angular expression, so you will probably want to quote it:

  • groupBy:'home' – groups items by their home property.
  • groupBy:home – looks for a variable called home in the current scope, gets its value, and groups items by a property with that name.

• Return value: The filter returns an array of group objects, one per group. Each object has:

  • a property items, whose value is an array of the items in that group;
  • a property with the same name as the group field (e.g. home in the above example), whose value is the name of that group.

• ng-repeat: To use this with ng-repeat, you need to supply a second argument ('peopleByHome' in the above example) which identifies the grouping being calculated. It should be unique within your app. If you see errors in the Javascript console about "10 digest iterations reached", check you haven't forgotten the second argument.

  It is used to cache the group objects returned by the filter, so that subsequent invocations can return the same objects, so that ng-repeat's digest cycle will correctly recognise the output has not changed.

• Ordering: The filter returns groups in the order they first appeared in the original array, and likewise items within each group in the same relative order as they appeared in the original array.

  If you want to control the ordering, sort the original array (e.g. using the standard orderBy filter) before passing it to groupBy:

  <div ng-repeat="placePeople in people | orderBy:'home' | groupBy:'home':'peopleByHome'">

• Performance: The filter itself should be reasonably efficient (O(n) in the number of items). However if used in an ng-repeat expression, the filter will be reevaluated on each digest cycle (e.g. when anything in the scope changes). Therefore if your original array may contain a lot of items, you may want to call this in your controller instead in order to precompute the grouping. (If so, you'll need explicit $watch statements if you want to update the grouping when the items change.)

  While the filter does some caching, it is only to avoid digest loops; subsequent runs will recompute the groupings from scratch (albeit avoiding the cost of object creation).

Reporting issues

If you have any problems using this, please submit an issue on Github and I will try to help.

Developing

Pull requests and constructive criticism gratefully accepted.

To hack on this, you'll need npm, bower and grunt. Then:

1. npm install
2. bower install
3. grunt – this will:
   • JSHint the code
   • run the Jasmine unit tests

I'll be more likely to accept a pull request that includes tests :)

Author

Sam Stokes

License

See LICENSE file.