Sort a multidimensional array descending by subarray count and preserve first level keys

Question

I have an array such as:

$array = [
    'DEF' => [
        ['type' => 1, 'id' => 1212, 'name' => 'Jane Doe', 'current' => 1],
        ['type' => 1, 'id' => 3123121, 'name' => 'Door', 'current' => null],
    ],
    'ABC' => [
        ['type' => 1, 'id' => 1234, 'name' => 'John Doe', 'current' => null],
    ],
    'WW' => [
        ['type' => 1, 'id' => 1212, 'name' => 'Jane Doe', 'current' => 1],
        ['type' => 1, 'id' => 3123121, 'name' => 'Door', 'current' => null],
        ['type' => 1, 'id' => 64646, 'name' => 'Floor', 'current' => null],
    ]
];

And I want to sort this array by number ( count() ) of inner-array items descending (i.e. most items first), so I will have this array:

[
    'WW' => [
        ['type' => 1, 'id' => 1212, 'name' => 'Jane Doe', 'current' => 1],
        ['type' => 1, 'id' => 3123121, 'name' => 'Door', 'current' => null],
        ['type' => 1, 'id' => 64646, 'name' => 'Floor', 'current' => null],
    ],
    'DEF' => [
        ['type' => 1, 'id' => 1212, 'name' => 'Jane Doe', 'current' => 1],
        ['type' => 1, 'id' => 3123121, 'name' => 'Door', 'current' => null],
    ],
    'ABC' => [
        ['type' => 1, 'id' => 1234, 'name' => 'John Doe', 'current' => null],
    ]
];

Can anyone suggest an efficient way to do so? Thanks.

Foremost

Why not usort php.net/manual/en/function.usort.php ? – Stannite

please use var_export for dumping arrays – Redbug

Answer 1

Using uksort:

uksort($array, function($a, $b) { return count($b) - count($a); });

Using array_multisort:

array_multisort(array_map('count', $array), SORT_DESC, $array);

---

With PHP < 5.3:

function sort_cb($a, $b) {
    return count($b) - count($a);
}
uksort($array, 'sort_cb');

Redbug

If you are using PHP < 5.3.0, you'll need to move that anonymous function out of there. – Mixie

you should not use PHP < 5.3.0 ;) – Redbug

The uksort() example didn't work as I lost my array keys ('ABC','DEF','WW') but the array_multisort() did work -- thanks! – Foremost

Shouldn't that be usort instead of uksort? – Pothead

uksort sorts by Keys. Keys cannot be arrays and count does not count anything. usort compares values, which can be arrays. – Morello

Answer 2

<?php
function cmp($a, $b)
{
    if ($a == $b) {
        return 0;
    }
    return (count($a) > count($b)) ? -1 : 1;
}

$a = array(
"AA" => array(
        array('type'=>'1', 'id'=>'2'),
        array('type'=>'2', 'id'=>'2')),
'BB' => array(
        array('type'=>'1', 'id'=>'2'),
        array('type'=>'2', 'id'=>'2'),
        array('type'=>'5', 'id'=>'2')),
'CC' => array(
        array('type'=>'1', 'id'=>'2'))
);  

usort($a, "cmp");

print_r($a);
?>

Anaplastic

If you use PHP 7, you can now just do count($a) <=> count($b); :) – Torr

This was exactly what I needed, thank you. – Weepy

Answer 3

$tempArr = $sortedArr = array();
foreach ($myArr as $k => $v) $tempArr[$k] = count($v);
asort($tempArr);
foreach ($tempArr as $k => $v) $sortedArr = $myArr[$k];

Note that this will break if any of the array values are not themselves arrays, you may want to add an is_array() check somewhere...

Meliorism

Answer 4

If you are only worried about sorting on size and not the actual quality, you can use the simplest approach to sort descending and preserve keys with arsort().

Array with fewer members is smaller, if key from operand 1 is not found in operand 2 then arrays are incomparable, otherwise - compare value by value (see following example)

In the event that you have multiple rows with the same size, then they will be further sorted descending based on their actual data.

Code: (Demo)

arsort($array);
var_export($array);

Cumulous