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.

Why not `usort` http://www.php.net/manual/en/function.usort.php ? — Joseph Silber, Sep 15 '11 at 15:42

Arnaud Le Blanc · Accepted Answer · 2011-09-15T15:58:50.333

40

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');

edited Sep 15 '11 at 15:58

answered Sep 15 '11 at 15:42

Arnaud Le Blanc

98,321
23
206
194

1

If you are using PHP < 5.3.0, you'll need to move that anonymous function out of there. – NullUserException Sep 15 '11 at 15:47
4

you should not use PHP < 5.3.0 ;) – Arnaud Le Blanc Sep 15 '11 at 15:50
The uksort() example didn't work as I lost my array keys ('ABC','DEF','WW') but the array_multisort() did work -- thanks! – Aviram Sep 15 '11 at 15:54
4

Shouldn't that be [usort](http://de1.php.net/usort) instead of [uksort](http://de1.php.net/uksort)? – Hirnhamster Aug 26 '14 at 14:33
2

`uksort` sorts by Keys. Keys cannot be arrays and count does not count anything. `usort` compares values, which can be arrays. – Grzegorz May 11 '18 at 11:15

score 4 · Answer 2 · answered Sep 15 '11 at 15:51

4

<?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);
?>

answered Sep 15 '11 at 15:51

Dan Bizdadea

1,292
8
15

If you use PHP 7, you can now just do `count($a) <=> count($b)`; :) – galdikas Jul 19 '17 at 05:53
This was exactly what I needed, thank you. – Aaron Jun 09 '21 at 07:35

score 1 · Answer 3 · answered Sep 15 '11 at 15:44

$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...

score 0 · Answer 4 · answered Oct 21 '22 at 02:28

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);

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

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