php - how to sort multiarray with the sub value -

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i have multidimensional array unexpected numbers of product groups

i want sort these groups lowest count number these groups

as example : first group after resort input product group because has lowest count number , input product group ..etc

how this?

<?php $a =  // output product group array(         array('id' => 117, 'name' => 'monitor', 'count' => 60),         array('id' => 118, 'name' => 'printer', 'count' => 16),         array('id' => 119, 'name' => 'sound card', 'count' => 19), // input product group   array(         array('id' => 120, 'name' => 'keyboard', 'count' => 11),         array('id' => 121, 'name' => 'hard', 'count' => 21),         array('id' => 122, 'name' => 'mouse', 'count' => 24)       )     )  ;        // code does't works // obtain list of columns foreach ($a $key => $row) {     $count[$key]  = $row['count']; } // sort data mid descending // add $data last parameter, sort common key  array_multisort($count, sort_asc, $a);   echo $count[$key]; ?>

i'm confused structure of $a. products 120-122 inside array sibling products 117-119. surely there should array wrapping "group" of 117-119? i'm going assume that's intended, otherwise makes no sense. should be:

$a = array(     array(         array('id' => 117, 'name' => 'monitor', 'count' => 60),         array('id' => 118, 'name' => 'printer', 'count' => 16),         array('id' => 119, 'name' => 'sound card', 'count' => 19),     ),     array(         array('id' => 120, 'name' => 'keyboard', 'count' => 11),         array('id' => 121, 'name' => 'hard', 'count' => 21),         array('id' => 122, 'name' => 'mouse', 'count' => 24),     ), );

now if understand correctly, want sort groups according lowest count of product inside group. can custom sort function so:

// first calculate lowest count each group foreach ($a $key => $group) {     $lowestcount = null;     foreach ($group $product) {         if ($lowestcount === null || $lowestcount > $product['count']) {             $lowestcount = $product['count'];         }     }     $a[$key]['lowestcount'] = $lowestcount; }  // sort groups according lowest count usort($a, function($group1, $group2) {     return $group1['lowestcount'] - $group2['lowestcount']; });  // clean 'lowestcount' variables foreach ($a $key => $group) unset($a[$key]['lowestcount']);

the output contain group of 120-122 first, group of 117-119, because 11 less 16. if that's not wanted, please clarify!

edit: old php (5.2 , below), change sort code to:

// sort groups according lowest count if (!function_exists('groupsort')) {     function groupsort($group1, $group2) {         return $group1['lowestcount'] - $group2['lowestcount'];     } } usort($a, 'groupsort');

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