Multidimensional indexed array to associative array depending on column value

Question

I have a multidimensional indexed array. Each element is an associative array with an id column which is unique between elements (its value never repeats within the array).

[indexed] =>Array
(
    [0] => Array
        (
            [id] => john
            [name] => John
            [age] => 29
        ),

    [1] => Array
        (
            [id] => peter
            [name] => Peter
            [age] => 30
        ),

    [2] => Array
        (
            [id] => harry
            [name] => Harry
            [age] => 19
        )
)

My goal is to convert this array into a multidimensional associative array, indexed by id values.

[indexed] =>Array
(
    [john] => Array
        (
            [id] => john
            [name] => John
            [age] => 29
        ),

    [peter] => Array
        (
            [id] => peter
            [name] => Peter
            [age] => 30
        ),

    [harry] => Array
        (
            [id] => harry
            [name] => Harry
            [age] => 19
        )
)

My best attempt so far is to loop over array elements and manually create the final array.

$associative = array();
foreach($indexed as $key=>$val) $associative[$val['id']] = $val;

I think it's not the most elegant solution. Is it possible to obtain the same result with built-in (more efficient) functions?

I think in PHP there is no inbuilt function which overwrites Key by a particular value in an array. If array count is not huge then this solution is OK. Otherwise use XML or JSON which is fast in processing — Mangesh Sathe
– Mangesh Sathe, Commented Oct 25, 2016 at 12:13

mickmackusa · Accepted Answer · 2022-03-08 02:09:00Z

The truth is php DOES offer a single, native function that allows you to replace the outer indexes with the values of a single column. The "magic" is in the 2nd parameter which tells php not to touch the subarray values when assigning the new keys.

Code: (Demo)

$indexed = [
    ['id' => 'john', 'name' => 'John', 'age' => 29],
    ['id' => 'peter', 'name' => 'Peter', 'age' => 30],
    ['id' => 'harry', 'name' => 'Harry', 'age' => 19],
];

var_export(array_column($indexed, null, 'id'));

Output:

array (
  'john' => 
  array (
    'id' => 'john',
    'name' => 'John',
    'age' => 29,
  ),
  'peter' => 
  array (
    'id' => 'peter',
    'name' => 'Peter',
    'age' => 30,
  ),
  'harry' => 
  array (
    'id' => 'harry',
    'name' => 'Harry',
    'age' => 19,
  ),
)

This even works on an array of objects. The end result is an array of objects with new, associative first-level keys. (Demo)

$indexed = [
    (object)['id' => 'john', 'name' => 'John', 'age' => 29],
    (object)['id' => 'peter', 'name' => 'Peter', 'age' => 30],
    (object)['id' => 'harry', 'name' => 'Harry', 'age' => 19],
];

var_export(array_column($indexed, null, 'id'));

Output:

array (
  'john' => 
  (object) array(
     'id' => 'john',
     'name' => 'John',
     'age' => 29,
  ),
  'peter' => 
  (object) array(
     'id' => 'peter',
     'name' => 'Peter',
     'age' => 30,
  ),
  'harry' => 
  (object) array(
     'id' => 'harry',
     'name' => 'Harry',
     'age' => 19,
  ),
)

Armin Sam · Accepted Answer · 2016-10-25 12:31:49Z

1

Here is another way of doing it (assuming $arr is your original array):

$associative = array_combine(array_map(function($item) { return $item['id']; }, $arr), $arr);

But I think using a foreach is still shorter and more readable compare to this.

answered Oct 25, 2016 at 12:31

Armin Sam

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