PHP usort Multi-dimensional array - php

Question

I'm having trouble getting usort to work and not sure what I'm missing. Below is an example of my array. I want to sort the array based on the value of the sort key.
Array
(
[0] => Array
(
[sort] => 1520546956
[row] => Data lives here
)
[1] => Array
(
[sort] => 1521047928
[row] => Data lives here
)
[2] => Array
(
[sort] => 1520525366
[row] => Data lives here
)
[3] => Array
(
[sort] => 1520525227
[row] => Data lives here
)
My code to try and sort this is:
foreach ($resultsArray as $record)
{
usort($record['sort'], function($a, $b)
{
if ($a == $b)
{
return 0;
}
return ($a < $b) ? -1 : 1;
});
}
However my code seems to be ineffective as the order of the array isn't changing. I feel like I'm close but can't identify what I'm missing. Thank you for any help!

Answer 1

A different approach to accomplish the same functionality is to use array_multisort with the desired combination of sorting flags.
Dataset:
$resultsArray = array(
array('sort'=>1520546956, 'row'=>'row 0 data'),
array('sort'=>1521047928, 'row'=>'row 1 data'),
array('sort'=>1520525366, 'row'=>'row 2 data'),
array('sort'=>1520525227, 'row'=>'row 3 data')
);
array_multisort Example:
$sortValues = array_column($resultsArray, 'sort');
array_multisort($sortValues, SORT_ASC, $resultsArray);
print_r($resultsArray);
Results: https://3v4l.org/NpVIc
Array
(
[0] => Array
(
[sort] => 1520525227
[row] => row 3 data
)
[1] => Array
(
[sort] => 1520525366
[row] => row 2 data
)
[2] => Array
(
[sort] => 1520546956
[row] => row 0 data
)
[3] => Array
(
[sort] => 1521047928
[row] => row 1 data
)
)
Alternatively you can still use usort, but in your function, you need to retrieve the associated array key named sort in order to compare the values.
usort Example:
usort($resultsArray, function($a, $b) {
if ($a['sort'] == $b['sort']) {
return 0;
}
return ($a['sort'] < $b['sort'] ? -1 : 1);
});
print_r($resultsArray);
Results: https://3v4l.org/5nfbc

Answer 2

Modified code to reflect the below as suggested:
usort($resultsArray, function($a, $b) { /* compare $a['sort'] and $b['sort'] */ }
Working perfectly.

Answer 3

$record['sort'] would have to be an array for that to work. Yet still, it does nothing.
I'm pretty sure you want to do this:
<?php
$multiArray = array(
array('sort'=>1520546956, 'row'=>'row 0 data'),
array('sort'=>1521047928, 'row'=>'row 1 data'),
array('sort'=>1520525366, 'row'=>'row 2 data'),
array('sort'=>1520525227, 'row'=>'row 3 data'));
foreach($multiArray as $a){
$numArray[] = $a['sort'];
}
asort($numArray, SORT_NUMERIC);
foreach($numArray as $k => $v){
$resArray[] = $multiArray[$k];
}
print_r($resArray);
?>

Answer 4

It is because php foreach construct works on the copy of the array provided(ie: $resultsArray), where php usort() function references or points to the same array. That is why your code is not working as expected.
If you don't understand this concept I suggest you a good online course by Kevin skoglund (php essential training) in Lynda.com