Sorting an associative array in PHP

Question

I have an array in this format:

Array
(
    [0] => Array
        (
            [text] => tests
            [language] => 
            [advertiserCompetitionScale] => 5
            [avgSearchVolume] => 7480000
            [lastMonthSearchVolume] => 9140000
        )

    [1] => Array
        (
            [text] => personality tests
            [language] => 
            [advertiserCompetitionScale] => 5
            [avgSearchVolume] => 165000
            [lastMonthSearchVolume] => 201000
        )

    [2] => Array
        (
            [text] => online tests
            [language] => 
            [advertiserCompetitionScale] => 5
            [avgSearchVolume] => 246000
            [lastMonthSearchVolume] => 301000
        )

)

How can I sort an array in that format, in the descending order of the avgSearchVolume field? Is there a built in function for this?

This is not an associative array ... but an array of associative arrays ;-) — Thomas Decaux, Jul 10 '12 at 10:56

score 111 · Accepted Answer · edited Oct 06 '11 at 11:54

111

Use usort and supply your own function to do the ordering, e.g.

function cmp($a, $b)
{
    return $b['avgSearchVolume'] - $a['avgSearchVolume'];
}

usort($array, "cmp");

edited Oct 06 '11 at 11:54

hakre

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answered Apr 22 '09 at 14:55

Paul Dixon

295,876
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And also reading http://stackoverflow.com/questions/8456029/how-does-usort-work#answer-8456055 also recomended – vinrav Dec 05 '14 at 09:29
1

Substitute `return strcmp($a['key'],$b['key']);` to compare strings – Jon Weers Mar 22 '17 at 20:50
1

`usort()` doesn't maintain the key association, use `uasort()` to maintain the key association. – luukvhoudt Feb 15 '18 at 16:39

score 18 · Answer 2 · answered Apr 22 '09 at 19:13

Until PHP 5.3 this is the best function for sorting based on subkeys without making a new function for each key.

function sortBySubkey(&$array, $subkey, $sortType = SORT_ASC) {
    foreach ($array as $subarray) {
        $keys[] = $subarray[$subkey];
    }
    array_multisort($keys, $sortType, $array);
}
sortBySubkey($arr, 'avgSearchVolume');

With PHP 5.3 you can make something like this, same function call as now.

function getSortVariable($sortType = SORT_ASC) {
    switch($sortType) {
        case SORT_ASC:
            return function ($a, $b) use ($subkey) { return strcmp($a[$subkey], $b[$subkey]); };
    }
}

function sortBySubkey(&$array, $subkey, $sortType = SORT_ASC) {
    $sortFunction = getSortVariable($sortType);
    usort($array, $sortFunction($subkey));
}

Stefan Gehrig · Answer 3 · 2009-04-22T15:00:09.240

8

You'll have to use a custom callback function together with usort().

function cmp($a, $b)
{
    if ($a['avgSearchVolume'] == $b['avgSearchVolume']) {
        return 0;
    }
    return ($a['avgSearchVolume'] > $b['avgSearchVolume']) ? -1 : 1;
}
usort($array, 'cmp');

edited Apr 22 '09 at 15:00

answered Apr 22 '09 at 14:54

Stefan Gehrig

82,642
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While that will work, a comparison function should really return 0 if two elements being compared are equal. – Paul Dixon Apr 22 '09 at 14:58
You're right Paul - but as the sort-order is undefined in case of equality, a better solution would be to introduce another comparison to remove this uncertainty. Edited the answer accordingly. – Stefan Gehrig Apr 22 '09 at 15:02

score 2 · Answer 4 · edited Dec 19 '16 at 15:58

2

function querySort ($first_Array,$second_Array) {
    return strcasecmp($first_Array['name'],$second_Array['name']);
}
echo '<pre>';
usort($main, 'querySort');

print_r($main);
die;

edited Dec 19 '16 at 15:58

Louis B.

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answered Feb 05 '14 at 09:36

dev4092

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A few words of explanation would make this code example even better. – Thom Apr 28 '14 at 11:18

score 1 · Answer 5 · answered Feb 20 '13 at 05:07

Here is another solution, You can add multiple options for sorting(See the commented section of the code)

<?php

$arr=Array(
     Array("text" => "tests","language" =>"","advertiserCompetitionScale" => 5,"avgSearchVolume" => 7480000,"lastMonthSearchVolume" => 9140000),
     Array("text" => "personality tests","language" =>"","advertiserCompetitionScale" => 5,"avgSearchVolume" => 165000,"lastMonthSearchVolume"=>201000),
     Array("text" => "online tests","language" =>"","advertiserCompetitionScale" => 5,"avgSearchVolume" => 246000,"lastMonthSearchVolume" =>301000)
     );


$sort = array();
foreach($arr as $k=>$v) {
    $sort['avgSearchVolume'][$k] = $v['avgSearchVolume'];
    //$sort['text'][$k] = $v['text'];
}

array_multisort($sort['avgSearchVolume'], SORT_DESC, $arr);
//array_multisort($sort['avgSearchVolume'], SORT_DESC, $sort['text'], SORT_ASC,$arr);

echo "<pre>";
print_r($arr);

?>

REF: http://php.net/manual/en/function.array-multisort.php

Sorting an associative array in PHP

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