PHP Sort a multidimensional array by number of items

Question

I have an array such as:

Array
(
    [DEF] => Array
        (
            [0] => Array
                (
                    [type] => 1
                    [id] => 1212
                    [name] => Jane Doe
                    [current] => 1
                )

            [1] => Array
                (
                    [type] => 1
                    [id] => 3123121
                    [name] => Door
                    [current] => 
                )
        )

    [ABC] => Array
        (
            [0] => Array
                (
                    [type] => 1
                    [id] => 1234
                    [name] => John Doe
                    [current] => 
                )
        )

    [WW] => Array
        (
            [0] => Array
                (
                    [type] => 1
                    [id] => 1212
                    [name] => Jane Doe
                    [current] => 1
                )

            [1] => Array
                (
                    [type] => 1
                    [id] => 3123121
                    [name] => Door
                    [current] => 
                )

            [2] => Array
                (
                    [type] => 1
                    [id] => 64646
                    [name] => Floor
                    [current] => 
                )
        )
)

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:

Array
(
    [WW] => Array
        (
            [0] => Array
                (
                    [type] => 1
                    [id] => 1212
                    [name] => Jane Doe
                    [current] => 1
                )

            [1] => Array
                (
                    [type] => 1
                    [id] => 3123121
                    [name] => Door
                    [current] => 
                )

            [2] => Array
                (
                    [type] => 1
                    [id] => 64646
                    [name] => Floor
                    [current] => 
                )
        )

    [DEF] => Array
        (
            [0] => Array
                (
                    [type] => 1
                    [id] => 1212
                    [name] => Jane Doe
                    [current] => 1
                )

            [1] => Array
                (
                    [type] => 1
                    [id] => 3123121
                    [name] => Door
                    [current] => 
                )
        )

    [ABC] => Array
        (
            [0] => Array
                (
                    [type] => 1
                    [id] => 1234
                    [name] => John Doe
                    [current] => 
                )
        )
)

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

39

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

95,062
22
198
192

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

1,294
8
13

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...

PHP Sort a multidimensional array by number of items

3 Answers3

Linked