How to Group Associative Array Rows by Column Value in PHP?

Grouping Associative ArrayRows by Column Value

In programming, you may encounter situations where you need to reorganize data stored in associative arrays. One common task is to group rows in the array by a specific column value while preserving the original first-level keys.

Consider the following associative array of associative arrays known as $old_arr:

[
    'a' => ['id' => 20, 'name' => 'chimpanzee'],
    'b' => ['id' => 40, 'name' => 'meeting'],
    'c' => ['id' => 20, 'name' => 'dynasty'],
    'd' => ['id' => 50, 'name' => 'chocolate'],
    'e' => ['id' => 10, 'name' => 'bananas'],
    'f' => ['id' => 50, 'name' => 'fantasy'],
    'g' => ['id' => 50, 'name' => 'football']
]

The goal is to create a new array, $arr, where rows are grouped based on the id field. The resulting array should look like this:

array
(
    10 => array
          (
            e => array ( id = 10, name = bananas )
          )
    20 => array
          (
            a => array ( id = 20, name = chimpanzee )
            c => array ( id = 20, name = dynasty )
          )
    40 => array
          (
            b => array ( id = 40, name = meeting )
          )
    50 => array
          (
            d => array ( id = 50, name = chocolate )
            f => array ( id = 50, name = fantasy )
            g => array ( id = 50, name = football )
          )
)

To achieve this, you can follow these steps:

1. Initialize an empty array $arr.
2. Iterate over each row in $old_arr.
3. Use the id value as a key in $arr. If the key does not exist, create a new array.
4. Assign the current row to the corresponding key in $arr.
5. Sort the $arr array by SORT_NUMERIC to ensure that the keys are in numerical order.

The provided PHP code follows this approach to generate the desired result:

$arr = array();

foreach ($old_arr as $key => $item) {
   $arr[$item['id']][$key] = $item;
}

ksort($arr, SORT_NUMERIC);

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