Example of array handling

example.php

<?php

/**
* [
*   [1, 1],
*   [1, 2],
*   [1, 3],
*   etc.
* ]
* to
* [1 => [
*   1,
*   2,
*   3,
*   etc.
* ]]
*/
$array = [[8, 2], [8, 3], [8, 5], [8, 8]];

$result = [];
array_walk($array, function ($item, $key) use (&$result) {
    $result[array_shift($item)][] = current($item); // or $item[0]
});

print_r($result);

// See DEMO: http://sandbox.onlinephpfunctions.com/code/453cc24d652fc0dc453a8feb13f16be5135b58cb