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 php.net/manual/en/function.usort.php ?

Joseph Silber
– Joseph Silber

2011-09-15 15:42:48 +00:00
Commented Sep 15, 2011 at 15:42 — Joseph Silber
– Joseph Silber, Commented Sep 15, 2011 at 15:42
please use var_export for dumping arrays

Arnaud Le Blanc
– Arnaud Le Blanc

2011-09-15 15:46:53 +00:00
Commented Sep 15, 2011 at 15:46 — Arnaud Le Blanc
– Arnaud Le Blanc, Commented Sep 15, 2011 at 15:46

Arnaud Le Blanc · Accepted Answer · 2011-09-15 15:58:50Z

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, 2011 at 15:58

answered Sep 15, 2011 at 15:42

Arnaud Le Blanc

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5 Comments

NullUserException Over a year ago

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

Arnaud Le Blanc Over a year ago

you should not use PHP < 5.3.0 ;)

Aviram Over a year ago

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

Hirnhamster Over a year ago

Shouldn't that be usort instead of uksort?

Grzegorz Over a year ago

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

Dan Bizdadea · Accepted Answer · 2011-09-15 15:51:09Z

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, 2011 at 15:51

Dan Bizdadea

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1 Comment

galdikas Over a year ago

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

DaveRandom · Accepted Answer · 2011-09-15 15:44:49Z

1

$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...

answered Sep 15, 2011 at 15:44

DaveRandom

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Comments

mickmackusa · Accepted Answer · 2022-10-21 02:28:06Z

0

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);

answered Oct 21, 2022 at 2:28

mickmackusa♦

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