PHP sort 2d array by index (non-associative)

This code does not run properly, but it suggests what I am trying to do:

function sort_2d_by_index($a,$i) {
  function cmp($x, $y) {
    // Nested function, can't find $i
    // (global $i defeats the purpose of passing an arg)
    if ($x[$i] == $y[$i]) { return 0; }
    return ($x[$i] < $y[$i]) ? -1 : 1;
  }

  usort($a,"cmp");
  return $a;
}

There HAS to be a much better way to do this. I've been examining ksort(), multisort(), and all sorts of sorts until I'm sort of t开发者_开发百科ired trying to sort it all out.

The situation is this: I've got a 2-d array...

array(
  array(3,5,7),
  array(2,6,8),
  array(1,4,9)
);

...and I want to sort by a column index. Say, column [1], would give this result:

array(
  array(1,4,9),
  array(3,5,7),
  array(2,6,8)
);

Does someone have a link (I'm sure this has been asked before), or could someone say "you need foosort, definitely". Thanks very much.

In the documentation of array_multisort it is mentioned that it can be used for this kind of thing.

You can't avoid creating an array that consists of only one column:

$sort_column = array();
foreach ($a as $row)
    $sort_column []= $row[1]; // 1 = your example

array_multisort($sort_column, $a);

This sorts both arrays synchronously so that afterwards your whole array is sorted in the same order as the $sort_column array is.

As of PHP 5.3 you can use a closure (pass $i into the function) by defining your cmp function like this:

$cmp = function($x, $y) use ($i) { ... };

You can use use to access $i:

function cmp($x, $y) use ($i) {
    // $i now available
    if ($x[$i] == $y[$i]) { return 0; }
    return ($x[$i] < $y[$i]) ? -1 : 1;
}

http://www.php.net/manual/en/function.sort.php#99419

phpdotnet at m4tt dot co dot uk

Simple function to sort an array by a specific key. Maintains index association.