PHP usort Multi-dimensional array

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!

$record will be a copy of the array element, not a reference. Thus, any changes you make to the element will not persist. To fix this, either do foreach($resultsArray as $index=>$record) and then $resultsArray[$index] = $record after sorting, or do foreach($resultsArray as &$record)--note the & in this second example! — B. Fleming
– B. Fleming, Commented Mar 20, 2018 at 23:49
Additionally, your sort logic itself is off. usort sorts the given array in place. Thus, $record['sort'] should be an array. If you want to use usort properly, do usort($resultsArray, function($a, $b) { /* compare $a['sort'] and $b['sort'] */ }! This will completely avoid the need for a foreach loop. — B. Fleming
– B. Fleming, Commented Mar 20, 2018 at 23:52
@B.Fleming That did the trick - ending up going with usort($resultsArray, function($a, $b) { /* compare $a['sort'] and $b['sort'] */ } and working correctly now. Thank you! — Jason
– Jason, Commented Mar 20, 2018 at 23:56

Will B. · Accepted Answer · 2018-03-21 00:44:21Z

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

Jason · Accepted Answer · 2018-03-20 23:57:44Z

0

Modified code to reflect the below as suggested:

usort($resultsArray, function($a, $b) { /* compare $a['sort'] and $b['sort'] */ }

Working perfectly.

answered Mar 20, 2018 at 23:57

Jason

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Comments

StackSlave · Accepted Answer · 2018-03-21 00:03:17Z

0

$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);
?>

answered Mar 21, 2018 at 0:03

StackSlave

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Comments

ajuchacko91 · Accepted Answer · 2018-07-04 07:33:17Z

0

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

edited Jul 4, 2018 at 7:33

answered Jul 3, 2018 at 18:03

ajuchacko91

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2 Comments

ajuchacko91 Over a year ago

@Oighea I have not asked any question but have answered it. clarify what you are trying to say.

Ṃųỻịgǻňạcểơửṩ Over a year ago

It isn't grammatically correct. Proper grammar is required since this isn't a chat room nor an informal discussion board.

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