Problems with sorting multidimensional array

Question

I try to sort a multidimensional array in the way, so that the elements with the same value should not being reordered.

This is the given array, which should be sorted by the value of type:

$arr = array(

    "a" => array(
        "type" => 1
    ),
    "d" => array(
        "type" => 1
    ),
    "super" => array(
        "type" => 2
    ),
    "c" => array(
        "type" => 1
    ),
    "b" => array(
        "type" => 1
    )

);

The sorted array should be look like this:

Array
(
    [super] => Array
        (
            [type] => 2
        )

    [a] => Array
        (
            [type] => 1
        )

    [d] => Array
        (
            [type] => 1
        )

    [c] => Array
        (
            [type] => 1
        )

    [b] => Array
        (
            [type] => 1
        )

)

use `arsort` to sort array. http://php.net/manual/en/function.arsort.php — Apb, Feb 17 '16 at 12:23
Possible duplicate of [How can I sort arrays and data in PHP?](http://stackoverflow.com/questions/17364127/how-can-i-sort-arrays-and-data-in-php) — Narendrasingh Sisodia, Feb 17 '16 at 12:31
you have shown a strange expected array. Why keys should go in such order: 'a' - 'c' -'b' ? And why is 'd' key missing? — RomanPerekhrest, Feb 17 '16 at 12:32

score 0 · Answer 1 · answered Feb 17 '16 at 12:34

Try a uasort: If you are still on PHP 5.2 or earlier, you'll have to define a sorting function first:

$myArray = array(

    "a" => array(
        "type" => 1
    ),
    "d" => array(
        "type" => 1
    ),
    "super" => array(
        "type" => 2
    ),
    "c" => array(
        "type" => 1
    ),
    "b" => array(
        "type" => 1
    )

);
function sortByOrder($a, $b)
{
    return $b['type'] - $a['type'];
}

uasort($myArray, 'sortByOrder');
print_r($myArray);

Starting in PHP 5.3, you can use an anonymous function:

uasort($myArray, function ($a, $b) {
    return $b['type'] - $a['type'];
});

And finally with PHP 7 you can use the "spaceship operator":

uasort($myArray, function ($a, $b) {
        return $b['type'] <=> $a['type'];
});

Output:

Array
(
    [super] => Array
        (
            [type] => 2
        )

    [b] => Array
        (
            [type] => 1
        )

    [c] => Array
        (
            [type] => 1
        )

    [a] => Array
        (
            [type] => 1
        )

    [d] => Array
        (
            [type] => 1
        )

)

Thanks for your answer, but the output is not that what I want: The difference is, that I want to keep the order of the elements with the same type. — Karsten, Feb 18 '16 at 11:12

score 0 · Answer 2 · edited May 23 '17 at 12:07

After browsing through the post (How can I sort arrays and data in PHP?)[How can I sort arrays and data in PHP?, I found a solution for my problem.

If the types are equal, I sort the elements into a static order, which I get from a second value id.

Array to sort:

$array = array(

    "a" => array(
        "id" => "a",
        "type" => 1
    ),
    "c" => array(
        "id" => "c",
        "type" => 1
    ),
    "super" => array(
        "id" => "super",
        "type" => 2
    ),
    "b" => array(
        "id" => "b",
        "type" => 1
    )

);

Script:

$sort_keys = array_column($array, "id");

function cmp($a, $b){

    global $sort_keys;

    if ($a["type"] < $b["type"]) {
        return 1;
    } else if ($a["type"] > $b["type"]) {
        return -1;
    } else {
        return array_search($a["_id"], $sort_keys) - array_search($b["_id"], $sort_keys);
    }

}

uasort($array, 'cmp');

I do have the field id in my script already, so I don’t even have to change my array.

Thanks to all who contribute to this post!

Can you suppose your algorithm effectiveness in O-notaion? – Max Zuber Feb 22 '16 at 08:22 — Max Zuber, Feb 22 '16 at 08:22

Max Zuber · Accepted Answer · 2016-02-23T06:30:32.840

0

I want to improve your own answer to exclude inefficient array_search(). It is better to index array items before sorting, and use it for equal types.

$index = 0;
foreach ($arr as $key => $value) {
  $arr[$key]['index'] = $index;
  $index++;
}

uasort($arr, function($a, $b) {
  if ($a['type'] < $b['type']) {
    return 1;
  } elseif ($a['type'] > $b['type']) {
    return -1;
  } else {
    return $a['index'] - $b['index'];
  }
});

foreach ($arr as $key => $value) {
  unset($arr[$key]['index']);
}

edited Feb 23 '16 at 06:30

answered Feb 22 '16 at 08:40

Max Zuber

1,166
9
15

Thanks for that – I now use your solution. The only thing I had to add, was a additional `foreach` loop to remove `'index'` after sorting. Maybe you can update your answer to reflect this. – Karsten Feb 22 '16 at 12:32

Problems with sorting multidimensional array

3 Answers3

Array to sort:

Script: