PHP
Group Array Elements by Specific Key
Learn to group an array of associative arrays by a common key's value, transforming flat data into a structured, grouped format.
<?php
$users = [
['id' => 1, 'name' => 'Alice', 'city' => 'New York'],
['id' => 2, 'name' => 'Bob', 'city' => 'Los Angeles'],
['id' => 3, 'name' => 'Charlie', 'city' => 'New York'],
['id' => 4, 'name' => 'David', 'city' => 'Chicago'],
['id' => 5, 'name' => 'Eve', 'city' => 'Los Angeles'],
];
function group_by_key(array $array, string $key): array {
$grouped = [];
foreach ($array as $item) {
if (isset($item[$key])) {
$grouped[$item[$key]][] = $item;
}
}
return $grouped;
}
$users_by_city = group_by_key($users, 'city');
// print_r($users_by_city);
/*
Expected output:
Array
(
[New York] => Array
(
[0] => Array
(
[id] => 1
[name] => Alice
[city] => New York
)
[1] => Array
(
[id] => 3
[name] => Charlie
[city] => New York
)
)
[Los Angeles] => Array
(
[0] => Array
(
[id] => 2
[name] => Bob
[city] => Los Angeles
)
[1] => Array
(
[id] => 5
[name] => Eve
[city] => Los Angeles
)
)
[Chicago] => Array
(
[0] => Array
(
[id] => 4
[name] => David
[city] => Chicago
)
)
)
*/
?>
How it works: This snippet provides a flexible function, `group_by_key`, to organize an array of associative arrays based on a specified key's value. It iterates through the input array, using the value of the chosen key (e.g., 'city') to create new top-level keys in the result. Each group then contains all original array elements that share that common key value, effectively transforming a flat list into a structured, categorized dataset.