Sort single-column rows of a 2d array by string prefix in a custom order then by string suffix naturally; and re-apply original keys to result

Question

I have a multidimensional array in this structure:

$arr = [
    0 => ['ref' => 'Q1'],
    1 => ['ref' => 'C6'],
    2 => ['ref' => 'C13'],
    3 => ['ref' => 'S3'],
    4 => ['ref' => 'Q11'],
    8 => ['ref' => 'S7'],
    9 => ['ref' => 'C4'],
];

I want to sort the array so that the order of values are S, Q, D, C, P, E and if possible have each alphanumeric ascending while also keeping the associate key [ref], like this:

$arr = [
    0 => ['ref' => 'S3'],
    1 => ['ref' => 'S7'],
    2 => ['ref' => 'Q1'],
    3 => ['ref' => 'Q11'],
    4 => ['ref' => 'C4'],
    8 => ['ref' => 'C6'],
    9 => ['ref' => 'C13'],
];

Are you missing keys 5, 6 and 7 on purpose, or was that a mistake? — Mike
– Mike, Commented Aug 16, 2018 at 8:26
usort and uasort both accept a user-defined comparison function, so they deal with whatever you tell them to deal with. — iainn
– iainn, Commented Aug 16, 2018 at 8:32

Nick · Accepted Answer · 2018-08-16 09:07:45Z

1

This code should do what you want. It uses usort with a compare function that first looks at the leading character and sorts that based on your specified order: S, Q, D, C, P, E. If the character is the same, it then compares the integer part of the value. Now the problem is that this loses the keys. We can't use uasort to get around that, as it will move the keys with the corresponding value. To get around that we first grab the keys of the array, then combine the keys with the sorted array at the end:

function mysort($a, $b) {
    $sort_order = ['S', 'Q', 'D', 'C', 'P', 'E'];
    // first, sort by leading character
    $s = array_search($a['ref'][0], $sort_order) - array_search($b['ref'][0], $sort_order);
    if ($s != 0) return $s;
    // if the same, sort by numeric part
    return (int)substr($a['ref'], 1) - (int)substr($b['ref'], 1);
}
$keys = array_keys($arr);
usort($arr, 'mysort');
$arr = array_combine($keys, $arr);

Output:

Array
(
    [0] => Array
        (
            [ref] => S3
        )
    [1] => Array
        (
            [ref] => S7
        )
    [2] => Array
        (
            [ref] => Q1
        )
    [3] => Array
        (
            [ref] => Q11
        )
    [4] => Array
        (
            [ref] => C4
        )
    [8] => Array
        (
            [ref] => C6
        )
    [9] => Array
        (
            [ref] => C13
        )
)

answered Aug 16, 2018 at 9:07

Nick

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1 Comment

Mike Over a year ago

Mine didn't use natural sorting like yours did, so it (probably) gives a wrong answer, unless that's how the OP wants it. And using array_combine is much better than creating an array of keys and looping over it, and creating a duplicate array. I actually wasn't aware of that function.

mickmackusa · Accepted Answer · 2025-01-31 22:04:33Z

For best performance, do not perform data preparations inside of the sorting algorithm. Calling array_search() inside of the sorting algorithm is not best practice.

array_multisort() Demo

$map = array_flip(
    ['S', 'Q', 'D', 'C', 'P', 'E']
);

foreach ($array as $keys[] => ['ref' => $v]) {
    sscanf($v, '%1s%d', $letter, $integers[]);
    $priorities[] = $map[$letter];
}
array_multisort(
    $priorities,
    $integers,
    $array
);
var_export(array_combine($keys, $array));

The less efficient version of above (because it calls sscanf() twice per iteration) using usort() looks like this: Demo

$map = array_flip(
    ['S', 'Q', 'D', 'C', 'P', 'E']
);

$keys = array_keys($array);

usort(
    $array,
    fn($a, $b) => [sscanf($a['ref'], '%1s%d', $letter, $integer), $map[$letter], $integer]
                  <=>
                  [sscanf($b['ref'], '%1s%d', $letter, $integer), $map[$letter], $integer]
);
var_export($array);

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