helpers\BaseArrayHelper index()

Indexes and/or groups the array according to a specified key.

The input should be either multidimensional array or an array of objects.

The $key can be either a key name of the sub-array, a property name of object, or an anonymous function that must return the value that will be used as a key.

$groups is an array of keys, that will be used to group the input array into one or more sub-arrays based on keys specified.

If the $key is specified as null or a value of an element corresponding to the key is null in addition to $groups not specified then the element is discarded.

For example:

$array = [
    ['id' => '123', 'data' => 'abc', 'device' => 'laptop'],
    ['id' => '345', 'data' => 'def', 'device' => 'tablet'],
    ['id' => '345', 'data' => 'hgi', 'device' => 'smartphone'],
];
$result = ArrayHelper::index($array, 'id');

The result will be an associative array, where the key is the value of id attribute

[
    '123' => ['id' => '123', 'data' => 'abc', 'device' => 'laptop'],
    '345' => ['id' => '345', 'data' => 'hgi', 'device' => 'smartphone']
    // The second element of an original array is overwritten by the last element because of the same id
]

An anonymous function can be used in the grouping array as well.

$result = ArrayHelper::index($array, function ($element) {
    return $element['id'];
});

Passing id as a third argument will group $array by id:

$result = ArrayHelper::index($array, null, 'id');

The result will be a multidimensional array grouped by id on the first level, by device on the second level and indexed by data on the third level:

[
    '123' => [
        ['id' => '123', 'data' => 'abc', 'device' => 'laptop']
    ],
    '345' => [ // all elements with this index are present in the result array
        ['id' => '345', 'data' => 'def', 'device' => 'tablet'],
        ['id' => '345', 'data' => 'hgi', 'device' => 'smartphone'],
    ]
]

The anonymous function can be used in the array of grouping keys as well:

$result = ArrayHelper::index($array, 'data', [function ($element) {
    return $element['id'];
}, 'device']);

The result will be a multidimensional array grouped by id on the first level, by the device on the second one and indexed by the data on the third level:

[
    '123' => [
        'laptop' => [
            'abc' => ['id' => '123', 'data' => 'abc', 'device' => 'laptop']
        ]
    ],
    '345' => [
        'tablet' => [
            'def' => ['id' => '345', 'data' => 'def', 'device' => 'tablet']
        ],
        'smartphone' => [
            'hgi' => ['id' => '345', 'data' => 'hgi', 'device' => 'smartphone']
        ]
    ]
]