Multidimensional indexed array to associative array depending on column value - php

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?

Answer 1

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,
),
)

Answer 2

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.