Question

I have an array like this

$users = array(
    [0] => array('Id' => 3, 'Name' => 'Bob'),
    [1] => array('Id' => 8, 'Name' => 'Alice'),
)

and I want to pull the Ids ‘up’ one level so that the final array is:

$usersById = array(
    [3] => array('Id' => 3, 'Name' => 'Bob'),
    [8] => array('Id' => 8, 'Name' => 'Alice'),
)

The Id values are unique.

Is there a native PHP way to do this? The code I’m currently using is:

$usersById = array();
foreach ($users as $key => $value)
{
    $usersById[$value['Id']] = $value;
}

This works, but is not terribly elegant.

Answer 1

Modern answer (requires PHP 5.5)

The new function array_column is very versatile and one of the things it can do is exactly this type of reindexing:

// second parameter is null means we 're just going to reindex the input
$usersById = array_column($users, null, 'Id');

Original answer (for earlier PHP versions)

You need to fetch the ids from the sub-arrays with array_map, then create a new array with array_combine:

$ids = array_map(function($user) { return $user['Id']; }, $users);
$users = array_combine($ids, $users);

The code above requires PHP >= 5.3 for the anonymous function syntax, but you can also do the same (albeit it will look a bit uglier) with create_function which only requires PHP >= 4.0.1:

$ids = array_map(create_function('$user', 'return $user["Id"];'), $users);
$users = array_combine($ids, $users);

See it in action.