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Selects a subset of items from `array` and returns it as a new array.

## Usage

### In HTML Template Binding

    {{ filter_expression | filter : expression : comparator : anyPropertyKey}}

### In JavaScript

    $filter('filter')(array, expression, comparator, anyPropertyKey)

### Arguments

Param | Type | Details
--- | --- | ---
array | Array | The source array. Note: If the array contains objects that reference themselves, filtering is not possible.
expression | string Object function() | The predicate to be used for selecting items from `array`. Can be one of: `string`: The string is used for matching against the contents of the `array`. All strings or objects with string properties in `array` that match this string will be returned. This also applies to nested object properties. The predicate can be negated by prefixing the string with `!`. `Object`: A pattern object can be used to filter specific properties on objects contained by `array`. For example `{name:"M", phone:"1"}` predicate will return an array of items which have property `name` containing "M" and property `phone` containing "1". A special property name (`$` by default) can be used (e.g. as in `{$: "text"}`) to accept a match against any property of the object or its nested object properties. That's equivalent to the simple substring match with a `string` as described above. The special property name can be overwritten, using the `anyPropertyKey` parameter. The predicate can be negated by prefixing the string with `!`. For example `{name: "!M"}` predicate will return an array of items which have property `name` not containing "M". Note that a named property will match properties on the same level only, while the special `$` property will match properties on the same level or deeper. E.g. an array item like `{name: {first: 'John', last: 'Doe'}}` will not be matched by `{name: 'John'}`, but will be matched by `{$: 'John'}`. `function(value, index, array)`: A predicate function can be used to write arbitrary filters. The function is called for each element of the array, with the element, its index, and the entire array itself as arguments. The final result is an array of those elements that the predicate returned true for.
comparator (optional) | function(actual, expected)true false | Comparator which is used in determining if values retrieved using `expression` (when it is not a function) should be considered a match based on the expected value (from the filter expression) and actual value (from the object in the array). Can be one of: `function(actual, expected)`: The function will be given the object value and the predicate value to compare and should return true if both values should be considered equal. `true`: A shorthand for `function(actual, expected) { return angular.equals(actual, expected)}`. This is essentially strict comparison of expected and actual. `false`: A short hand for a function which will look for a substring match in a case insensitive way. Primitive values are converted to strings. Objects are not compared against primitives, unless they have a custom `toString` method (e.g. `Date` objects). Defaults to `false`.
anyPropertyKey (optional) | string | The special property name that matches against any property. By default `$`.

## Examples

    <div ng-init="friends = [{name:'John', phone:'555-1276'},
                             {name:'Mary', phone:'800-BIG-MARY'},
                             {name:'Mike', phone:'555-4321'},
                             {name:'Adam', phone:'555-5678'},
                             {name:'Julie', phone:'555-8765'},
                             {name:'Juliette', phone:'555-5678'}]"></div>

    <label>Search: <input ng-model="searchText"></label>
    <table id="searchTextResults">
      <tr><th>Name</th><th>Phone</th></tr>
      <tr ng-repeat="friend in friends | filter:searchText">
        <td>{{friend.name}}</td>
        <td>{{friend.phone}}</td>
      </tr>
    </table>
    <hr>
    <label>Any: <input ng-model="search.$"></label> <br>
    <label>Name only <input ng-model="search.name"></label><br>
    <label>Phone only <input ng-model="search.phone"></label><br>
    <label>Equality <input type="checkbox" ng-model="strict"></label><br>
    <table id="searchObjResults">
      <tr><th>Name</th><th>Phone</th></tr>
      <tr ng-repeat="friendObj in friends | filter:search:strict">
        <td>{{friendObj.name}}</td>
        <td>{{friendObj.phone}}</td>
      </tr>
    </table>

    var expectFriendNames = function(expectedNames, key) {
      element.all(by.repeater(key + ' in friends').column(key + '.name')).then(function(arr) {
        arr.forEach(function(wd, i) {
          expect(wd.getText()).toMatch(expectedNames[i]);
        });
      });
    };

    it('should search across all fields when filtering with a string', function() {
      var searchText = element(by.model('searchText'));
      searchText.clear();
      searchText.sendKeys('m');
      expectFriendNames(['Mary', 'Mike', 'Adam'], 'friend');

      searchText.clear();
      searchText.sendKeys('76');
      expectFriendNames(['John', 'Julie'], 'friend');
    });

    it('should search in specific fields when filtering with a predicate object', function() {
      var searchAny = element(by.model('search.$'));
      searchAny.clear();
      searchAny.sendKeys('i');
      expectFriendNames(['Mary', 'Mike', 'Julie', 'Juliette'], 'friendObj');
    });
    it('should use a equal comparison when comparator is true', function() {
      var searchName = element(by.model('search.name'));
      var strict = element(by.model('strict'));
      searchName.clear();
      searchName.sendKeys('Julie');
      strict.click();
      expectFriendNames(['Julie'], 'friendObj');
    });