php array sorting on child element

Question

I am trying to sort an array based on the first [0] child element. But in my code the keys are being replaced by the array number in the sort:

$myArray = array(
    'my last row' => array(  
         '0' => 'ZZZZ',
         '1' => 'AAAA'
     ),
     'the first row' => array(
         '0' => 'AAAA'
     )
  );
usort($myArray, 'cmp' ) ;

var_dump($myArray);

function cmp    ($a, $b)        {
        return ( ( $a[0] > $b[0] ) ? 1 : -1 );
}

result:

array(2) {
  [0]=>       // should be ['the first row']  *not* [0]
  array(1) {
    [0]=>
    string(4) "AAAA"
  }
  [1]=>        // should be ['my last row']  *not* [1]
  array(2) {
    [0]=>
    string(4) "ZZZZ"
    [1]=>
    string(4) "AAAA"
  }
}

The sort order itself appears to be working as expected.

I would like to see the following:

the first row  => AAAA
my last row   =>  ZZZZ, AAAA

This is probably a very simple issue, but I cannot resolve it.

Thank you very much.

EDIT: this sort does not involve the key itself, but rather a child-element key. i believe that makes this question unique.

Possible duplicate of Keeping array index key when sorting a multidimensional array with PHP — Don't Panic
– Don't Panic, Commented Jul 11, 2017 at 20:22
"Don't Panic"'s suggestion of using "uasort" worked great, but he seemed to have removed his answer. if you want to put it out there again, i would be honored to select that as the correct one. — edwardsmarkf
– edwardsmarkf, Commented Jul 11, 2017 at 20:29
@edwardsmarkf I deleted it after I found what I thought was a duplicate. It still looks like a duplicate to me, to be honest. Maybe take a look at that one again? Their comparison function is different, but the main point of it is that they're having the same issue with the keys not being preserved. — Don't Panic
– Don't Panic, Commented Jul 11, 2017 at 20:34
Dont Panic - you are correct it was a duplicate, sorry. But your solution worked out great. Sadly, i have discovered this takes a HUGE performance hit, so i am looking into doing the sort on the client side instead. — edwardsmarkf
– edwardsmarkf, Commented Jul 11, 2017 at 23:21

Difster · Accepted Answer · 2017-07-11 19:41:46Z

0

Try this: It will maintain your index associations.

$myArray = array(
'my last row' => array(  
     '0' => 'ZZZZ',
     '1' => 'AAAA'
 ),
 'the first row' => array(
     '0' => 'AAAA'
 )

); asort($myArray);

print_r($myArray);

Array ( [the first row] => Array ( [0] => AAAA ) [my last row] => Array ( [0] => ZZZZ [1] => AAAA ) )

answered Jul 11, 2017 at 19:41

Difster

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