Group values in an array of single-element arrays by second level key and sum values within each group

Question

The input array:

[
    [1 => 2],
    [1 => 2],
    [2 => 1],
    [3 => 1],
]

I want this output:

[
    [1 => 4],
    [2 => 1],
    [3 => 1],
]

Answer 1

$result = array();
foreach ($input as $subarray) {
    foreach ($subarray as $key => $value) {
        if (isset($result[$key])) {
            $result[$key][$key] += $value;
        } else {
            $result[$key] = array($key => $value);
        }
    }
}
$result = array_values($result); // Convert from associative array to indexed array