PHP array_column: Extract Column from Multidimensional Array

Extracting a single column of values from a multidimensional array is a common task in PHP development. This article provides a quick and clear guide on how to use PHP’s built-in array_column() function to accomplish this task efficiently, complete with practical code examples.

Understanding array_column()

The array_column() function returns the values from a single column of an input array, typically a multidimensional array or an array of objects. It eliminates the need for writing verbose foreach loops to isolate specific data.

Syntax

array_column(array $input, int|string|null $column_key, int|string|null $index_key = null): array

• $input: The multidimensional array (or array of objects) from which to draw values.
• $column_key: The key of the column of values you want to extract. Pass null to return complete arrays or objects (useful when resetting array keys using the third parameter).
• $index_key: (Optional) The column to use as the index/keys for the returned array.

Practical Examples

1. Basic Column Extraction

To extract a simple list of values from a specific key, pass the multidimensional array as the first argument and the key name as the second argument.

$users = [
    ['id' => 101, 'name' => 'Alice', 'role' => 'Admin'],
    ['id' => 102, 'name' => 'Bob', 'role' => 'Editor'],
    ['id' => 103, 'name' => 'Charlie', 'role' => 'User']
];

// Extract all names
$names = array_column($users, 'name');

print_r($names);

Output:

Array
(
    [0] => Alice
    [1] => Bob
    [2] => Charlie
)

2. Extracting a Column with Custom Keys

You can use the third parameter to define custom keys for the returned array. This is highly useful for re-indexing arrays by a unique identifier.

$users = [
    ['id' => 101, 'name' => 'Alice', 'role' => 'Admin'],
    ['id' => 102, 'name' => 'Bob', 'role' => 'Editor'],
    ['id' => 103, 'name' => 'Charlie', 'role' => 'User']
];

// Extract names indexed by user ID
$namesById = array_column($users, 'name', 'id');

print_r($namesById);

Output:

Array
(
    [101] => Alice
    [102] => Bob
    [103] => Charlie
)

3. Extracting from an Array of Objects

array_column() also works seamlessly with arrays of objects. It can access public properties of objects directly.

class User {
    public $id;
    public $username;

    public function __construct($id, $username) {
        $this->id = $id;
        $this->username = $username;
    }
}

$users = [
    new User(1, 'johndoe'),
    new User(2, 'janedoe'),
];

$usernames = array_column($users, 'username');

print_r($usernames);

Output:

Array
(
    [0] => johndoe
    [1] => janedoe
)