Question

I am trying to sort a multi dimensional array, and have one value always at the end of the array. The array should be sorted by ‘unitText’ (dont care how unitID is sorted), but always have “Last” as the last value in the array. I’ve almost got it, but not quite there.

<?php

function cmp($a, $b)
{
    /*
    $a = preg_replace('@^(Last) @', '', $a);
    $b = preg_replace('@^(Last) @', '', $b);
    return strcasecmp($a, $b);
    */

    if(strtolower(substr($a['unitText'],0,4))=="last") return strnatcmp($a['unitText'],9999);
    else if(strtolower(substr($b['unitText'],0,4))=="last") return strnatcmp(9999,$b['unitText']);
    else return strnatcmp($a, $b);

    //return strnatcmp($a['unitText'], $b['unitText']);

    //return end($a) > end($b);

}

$unit = array(
    array("unitID"=>80, "unitText"=>"Q701"),
    array("unitID"=>30, "unitText"=>"H568"),
    array("unitID"=>25, "unitText"=>"Last"),
    array("unitID"=>40, "unitText"=>"Z255"),
    array("unitID"=>20, "unitText"=>"A459")
);

echo "<pre>";
print_r($unit);
echo "</pre>";

echo "<hr/>";

//uksort($unit['unitText'], "cmp");
//array_multisort($unit['unitText'], SORT_DESC, $unit['unitID'], SORT_ASC, $unit);
usort($unit, 'cmp');

echo "<pre>";
print_r($unit);
echo "</pre>";

?>

Should end up with:

Array
(
    [0] => Array
        (
            [unitID] => 20
            [unitText] => A459
        )

    [1] => Array
        (
            [unitID] => 30
            [unitText] => H568
        )

    [2] => Array
        (
            [unitID] => 80
            [unitText] => Q701
        )

    [3] => Array
        (
            [unitID] => 40
            [unitText] => Z255
        )

    [4] => Array
        (
            [unitID] => 25
            [unitText] => Last
        )

)

What am I doing wrong?

Answer 1

Your problem is with this line:

else return strnatcmp($a, $b);

Remember that $a and $b are both arrays, but strnatcmp() compares strings. When this function is called, your two arrays will be implicitly cast to strings, which will both have the value of Array, so they will return as equal and will not be sorted.

You should be comparing the unitText value:

else return strnatcmp($a['unitText'], $b['unitText'])

The fact that you didn’t see this tells me that you don’t have your error_reporting level set high enough in development, since that implicit cast issues an E_NOTICE when it occurs. In development, you should always have error_reporting(E_ALL | E_STRICT); set (either at the entry point for your code, or in your php.ini, etc.) so that any little issues get immediately flagged for you to fix.

Also, there is no reason why you should be calling strnatcmp() at all when one of the values is ‘Last’, because you already know that the value should be last. Just return 1 or -1 (depending on which contains ‘Last’) and be done with it.

Finally, you don’t need all the else conditions in the code. Since all paths issue a return, you can assume that anything that comes after an if block is only executed if the comparison fails:

if (strtolower(substr($a['unitText'],0,4))=="last") {
  return 1;
}

if strtolower(substr($b['unitText'],0,4))=="last") {
  return -1;
}

return strnatcmp($a['unitText'], $b['unitText']);

In the above, the second if only executes if we didn’t find ‘Last’ within $a, since the function would have already ended if it had. Similarly, the final return statement (with the strnatcmp() call) only executes if neither of the above if conditions passed, because either one of them would have returned a value and ended the function.

It’s a little thing, but nesting a bunch of unneeded if and else blocks makes the code less readable.