array_multisort ...... help!!

simulant

Ok, I have an array, and I want to sort by a specific column. Here's the array:


$arr = array(
  array(
    "ReportNumber" => "rpt099",
    "Column2" => "asdf"
  ),
  array(
    "ReportNumber" => "rpt057",
    "Column2" => "zyxw"
  ),
);

How do I sort the array by "ReportNumber"??

This is what I've been trying:


// let $column = 0 (sort by the first column)
// and $sortorder = SORT_ASC

foreach ($arr as $a) {
  $keys = array_keys($a);
  $sortarr[][$keys[$column]] = $a[$keys[$column]];
}
array_multisort($sortarr, $sortoder, $arr, $sortorder);

.....but this is not changing the array at all!!

mahers

This question was asked fairly recently. Maybe the usort() function is what you were after?

Weedpacket

It depends on how you're viewing the resulting $sortarr in a way - multisort retains key associations, so that whatever $sortarr[4] is associated with before the sort, it's still associated with it afterward. Hence a for() loop that runs over those keys will pick up records in the same order before and after the sort.

But you can re-key the records by going array_values(). Do that after multisorting, and see if that changes things.

But personally, I tend to go along with maher's suggestion: usort is (I feel) more intuitive.

simulant

The only problem I have with using usort() is that the comparison function doesn't seem to allow any more parameters besides the two values that you are comparing. I don't want to have to hard-code the index that I'm sorting on in the comparison function, so I want to pass it in as a parameter, as well as the sort order (asc or desc).

This is the thought sequence:

// I don't want to hard-code the indexes!
function cmp($a, $b) {
  return strcmp($a["ReportNumber"], $b["ReportNumber"]);
}

// So I need to do something like this, since I never know
// what index we will be sorting on
function cmp($index, $a, $b) {
  return strcmp($a[$index], $b[$index]);
}

// And better yet, I need to pass in the sort order
function cmp($index, $a, $b, $order='asc') {
  if ($order == 'asc') return strcmp($a[$index], $b[$index]);
  else return !strcmp($a[$index], $b[$index]);
}

// Then, of course, usort() is called....but how can you pass
// parameters to "cmp"??
usort($arr, "cmp");

Thanks for your help.....

simulant

Any ideas??

Weedpacket

Originally posted by simulant
Any ideas??

But you can re-key the records by going array_values(). Do that after multisorting, and see if that changes things.

simulant

I'm sorry, could you explain a little more of what you mean? I am not seeing this....

Thanks.

simulant

Ok, I figured it out.....FINALLY!!

My code was almost correct.....$sortarr changed a little bit, but the real problem is that the array arguments to array_multisort() MUST be passed by reference in order for this to work!!

Instead of this:

foreach ($arr as $a) {
  $keys = array_keys($a);
  $sortarr[][$keys[$column]] = $a[$keys[$column]];
}
array_multisort($sortarr, $sortoder, $arr, $sortorder);

Do this:

foreach ($arr as $a) {
  $keys = array_keys($a);
  $sortarr[] = $a[$keys[$column]];
}
array_multisort(&$sortarr, $sortoder, &$arr, $sortorder);

Gotta love those user-contributed notes in the PHP manual....

if you're having problems with array_multisort changing variables in global space when it is called inside a function and you're not passing in the function parameters by reference you can alleviate the problem by calling array_multisort with its parameters by reference, eg, array_multisort(&$a, SORT_DESC, &$b);

So here is a general function to handle multi-dimensional array sorting by a specific column and order:

function array_csort(&$arr, $column=0, $order='asc') {
  $order = ($order == 'asc') ? SORT_ASC : SORT_DESC;  

  foreach ($arr as $a) {
    $keys = array_keys($a);
    $sortarr[] = $a[$keys[$column]];
  }
  array_multisort(&$sortarr, $order, &$arr, $order);
} // array_csort

cdxrevvved

ty ty ty

This solved one of my issues... 🙂