Sorting Multidimensional and Multiple Arrays with array_multisort

This tutorial covers the following topics:

1. The array_multisort function
2. Sorting multiple arrays based on each other.
3. Sorting multidimensional arrays.

<?php
//Syntax
array_multisort(
    array &$array1,
    mixed $array1_sort_order = SORT_ASC,
    mixed $array1_sort_flags = SORT_REGULAR,
    mixed ...$rest
): bool

1. $array1
   The first argument to array_multisort() is the array that you want to sort first.
2. $array_sort_order (optional)
   Use the constant SORT_ASC or SORT_DESC for ascending or descending, respectively. The default sorting order is SORT_ASC.
3. $array1_sort_flags (optional)
   You can also use the sorting flags to change the sorting behavior. Click to read about the list of sort_flags constants.
4. …$rest
   Other arrays that you want to be sorted in sync with the first. Each subsequent array can also be followed by the optional arguments (sort_order and sort_flags).

Example: array_multisort

<?php
array_multisort($arr1, SORT_DESC, SORT_STRING,
                $arr2, SORT_NUMERIC,
                $arr3, SORT_STRING,
                $arr4, SORT_ASC, SORT_NATURAL,
                $arr5);

Sorting Mulitple Arrays

The array_multisort() function accepts multiple arrays and uses them as sort criteria. Sorting begins with the first array; values in that array that evaluate as equal are sorted by the next array, and so on.

<?php
 $array1 = ['one', 'two', 'three'];
 $array2 = ['I', 'II', 'III'];
 $array3 = [1, 2 , 3];

 array_multisort($array1,
                 $array2, 
                 $array3);

 print_r($array1);
 print_r($array2);
 print_r($array3);

In the above example, arrays keep in sync when reordered. The following output prints on the browser:

Array
(
    [0] => one
    [1] => three
    [2] => two
)
Array
(
    [0] => I
    [1] => III
    [2] => II
)
Array
(
    [0] => 1
    [1] => 3
    [2] => 2
)

Sorting Multidimensional Arrays

This function comes in handy when dealing with symmetrical multidimensional arrays, like the one in the following example:

<?php
//Note: p key represents the population
$data = [
['city' => 'Tokyo',    'p' => '37,435,191'],
['city' => 'Delhi',    'p' => '29,399,141'],
['city' => 'Shanghai', 'p' => '26,317,104'],
['city' => 'Sao Paulo','p' => '21,846,507'],
['city' => 'Mexico City', 'p' => '21,671,908'],
['city' => 'Cairo',   'p' => '20,484,965'],
['city' => 'Dhaka',   'p' => '20,283,552'],
['city' => 'Mumbai',  'p' => '20,185,064'],
['city' => 'Beijing', 'p' => '20,035,455'],
['city' => 'Osaka',   'p' => '19,222,665']
];

We want the $data array to be sorted by cities in ascending order, to accomplish this, we need an array that contains the same cities name in the same order as in the $data array. This can be done easily by using the array_column function. The array_column takes two arguments: the array and the key you want to extract from the multidimensional array.

<?php
 //$data = [['city'=>'Tokyo, 'p' => '2...];
 $cities = array_column ($data, 'city');

Now we can use array_multisort() to sort the multidimensional array $data. The first argument needs to be the $cities array, followed by the sort direction, and then the $data array:

<?php
//Note: p key represents the population
$data = [
['city' => 'Tokyo',    'p' => '37,435,191'],
['city' => 'Delhi',    'p' => '29,399,141'],
['city' => 'Shanghai', 'p' => '26,317,104'],
['city' => 'Sao Paulo','p' => '21,846,507'],
['city' => 'Mexico City', 'p' => '21,671,908'],
['city' => 'Cairo',   'p' => '20,484,965'],
['city' => 'Dhaka',   'p' => '20,283,552'],
['city' => 'Mumbai',  'p' => '20,185,064'],
['city' => 'Beijing', 'p' => '20,035,455'],
['city' => 'Osaka',   'p' => '19,222,665']
];

$cities = array_column ($data, 'city');

array_multisort($cities, SORT_ASC,
                $data);
foreach ($data as $v){
 echo $v['city'] .' : '. $v['p'];
 echo '<br>';
}

Edit the above code if you want to sort the $data array by population, and replace relevant lines with the following code:

<?php

$population = array_column ($data, 'p');
array_multisort($population, SORT_ASC,
                $data);

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