array_multisort

Sort multiple or multi-dimensional arrays

&reftitle.description; `bool` `array_multisort` `array` `array1` `mixed` `array1_sort_order` SORT_ASC `mixed` `array1_sort_flags` SORT_REGULAR `mixed` `rest`

`array_multisort` can be used to sort several arrays at once, or a multi-dimensional array by one or more dimensions.

Associative (`string`) keys will be maintained, but numeric keys will be re-indexed.

¬e.sort-unstable; ¬e.reset-index;
&reftitle.parameters;

`array1`

- An `array` being sorted.

`array1_sort_order`

- The order used to sort the previous `array` argument. Either `SORT_ASC` to sort ascendingly or `SORT_DESC` to sort descendingly.

  This argument can be swapped with `array1_sort_flags` or omitted entirely, in which case `SORT_ASC` is assumed.

`array1_sort_flags`

- Sort options for the previous `array` argument:

  Sorting type flags:

  - `SORT_REGULAR` - compare items normally (don't change types)

  - `SORT_NUMERIC` - compare items numerically

  - `SORT_STRING` - compare items as strings

  - `SORT_LOCALE_STRING` - compare items as strings, based on the current locale. It uses the locale, which can be changed using `setlocale`

  - `SORT_NATURAL` - compare items as strings using "natural ordering" like `natsort`

  - `SORT_FLAG_CASE` - can be combined (bitwise OR) with `SORT_STRING` or `SORT_NATURAL` to sort strings case-insensitively

  This argument can be swapped with `array1_sort_order` or omitted entirely, in which case `SORT_REGULAR` is assumed.

`rest`

- More arrays, optionally followed by sort order and flags. Only elements corresponding to equivalent elements in previous arrays are compared. In other words, the sort is lexicographical.

&reftitle.returnvalues;

&return.success;

&reftitle.examples;

### Sorting multiple arrays

    <?php
    $ar1 = array(10, 100, 100, 0);
    $ar2 = array(1, 3, 2, 4);
    array_multisort($ar1, $ar2);

    var_dump($ar1);
    var_dump($ar2);
    ?>

In this example, after sorting, the first array will contain 0, 10, 100, 100. The second array will contain 4, 1, 2, 3. The entries in the second array corresponding to the identical entries in the first array (100 and 100) were sorted as well.

    array(4) {
      [0]=> int(0)
      [1]=> int(10)
      [2]=> int(100)
      [3]=> int(100)
    }
    array(4) {
      [0]=> int(4)
      [1]=> int(1)
      [2]=> int(2)
      [3]=> int(3)
    }

### Sorting multi-dimensional array

    <?php
    $ar = array(
           array("10", 11, 100, 100, "a"),
           array(   1,  2, "2",   3,   1)
          );
    array_multisort($ar[0], SORT_ASC, SORT_STRING,
                    $ar[1], SORT_NUMERIC, SORT_DESC);
    var_dump($ar);
    ?>

In this example, after sorting, the first array will transform to "10", 100, 100, 11, "a" (it was sorted as strings in ascending order). The second will contain 1, 3, "2", 2, 1 (sorted as numbers, in descending order).

    array(2) {
      [0]=> array(5) {
        [0]=> string(2) "10"
        [1]=> int(100)
        [2]=> int(100)
        [3]=> int(11)
        [4]=> string(1) "a"
      }
      [1]=> array(5) {
        [0]=> int(1)
        [1]=> int(3)
        [2]=> string(1) "2"
        [3]=> int(2)
        [4]=> int(1)
      }
    }

### Sorting database results

For this example, each element in the `data` array represents one row in a table. This type of dataset is typical of database records.

Example data:

    volume | edition
    -------+--------
        67 |       2
        86 |       1
        85 |       6
        98 |       2
        86 |       6
        67 |       7

The data as an array, called `data`. This would usually, for example, be obtained by looping with `mysqli_fetch_assoc`.

    <?php
    $data[] = array('volume' => 67, 'edition' => 2);
    $data[] = array('volume' => 86, 'edition' => 1);
    $data[] = array('volume' => 85, 'edition' => 6);
    $data[] = array('volume' => 98, 'edition' => 2);
    $data[] = array('volume' => 86, 'edition' => 6);
    $data[] = array('volume' => 67, 'edition' => 7);
    ?>

In this example, we will order by `volume` descending, `edition` ascending.

We have an array of rows, but `array_multisort` requires an array of columns, so we use the below code to obtain the columns, then perform the sorting.

    <?php
    // Obtain a list of columns
    foreach ($data as $key => $row) {
        $volume[$key]  = $row['volume'];
        $edition[$key] = $row['edition'];
    }

    // you can use array_column() instead of the above code
    $volume  = array_column($data, 'volume');
    $edition = array_column($data, 'edition');

    // Sort the data with volume descending, edition ascending
    // Add $data as the last parameter, to sort by the common key
    array_multisort($volume, SORT_DESC, $edition, SORT_ASC, $data);
    ?>

The dataset is now sorted, and will look like this:

    volume | edition
    -------+--------
        98 |       2
        86 |       1
        86 |       6
        85 |       6
        67 |       2
        67 |       7

### Case insensitive sorting

Both `SORT_STRING` and `SORT_REGULAR` are case sensitive, strings starting with a capital letter will come before strings starting with a lowercase letter.

To perform a case insensitive sort, force the sorting order to be determined by a lowercase copy of the original array.

    <?php
    $array = array('Alpha', 'atomic', 'Beta', 'bank');
    $array_lowercase = array_map('strtolower', $array);

    array_multisort($array_lowercase, SORT_ASC, SORT_STRING, $array);

    print_r($array);
    ?>

&example.outputs;

    Array
    (
        [0] => Alpha
        [1] => atomic
        [2] => bank
        [3] => Beta
    )

&reftitle.seealso;

- `usort`
- &seealso.array.sorting;