How to sort an array of associative arrays by value of a given key in PHP?

Given this array:

$inventory = array(

   array("type"=>"fruit", "price"=>3.50),
   array("type"=>"milk", "price"=>2.90),
   array("type"=>"pork", "price"=>5.43),

);

I would like to sort $inventory's elements by price to get:

$inventory = array(

   array("type"=>"pork", "price"=>5.43),
   array("type"=>"fruit", "price"=>3.50),
   array("type"=>"milk", "price"=>2.90),

);

How can I do this?

You are right, the function you're looking for is array_multisort().

Here's an example taken straight from the manual and adapted to your case:

$price = array();
foreach ($inventory as $key => $row)
{
    $price[$key] = $row['price'];
}
array_multisort($price, SORT_DESC, $inventory);

As of PHP 5.5.0 you can use array_column() instead of that foreach:

$price = array_column($inventory, 'price');

array_multisort($price, SORT_DESC, $inventory);

PHP 7+

As of PHP 7, this can be done concisely using usort with an anonymous function that uses the spaceship operator to compare elements.

You can do an ascending sort like this:

usort($inventory, function ($item1, $item2) {
    return $item1['price'] <=> $item2['price'];
});

Or a descending sort like this:

usort($inventory, function ($item1, $item2) {
    return $item2['price'] <=> $item1['price'];
});

To understand how this works, note that usort takes a user-provided comparison function that must behave as follows (from the docs):

> The comparison function must return an integer less than, equal to, or greater than zero if the first argument is considered to be respectively less than, equal to, or greater than the second.

And note also that <=>, the spaceship operator,

> returns 0 if both operands are equal, 1 if the left is greater, and -1 if the right is greater

which is exactly what usort needs. In fact, almost the entire justification given for adding <=> to the language in https://wiki.php.net/rfc/combined-comparison-operator is that it

> makes writing ordering callbacks for use with usort() easier

---

PHP 5.3+

PHP 5.3 introduced anonymous functions, but doesn't yet have the spaceship operator. We can still use usort to sort our array, but it's a little more verbose and harder to understand:

usort($inventory, function ($item1, $item2) {
    if ($item1['price'] == $item2['price']) return 0;
    return $item1['price'] < $item2['price'] ? -1 : 1;
});

Note that although it's fairly common for comparators dealing with integer values to just return the difference of the values, like $item2['price'] - $item1['price'], we can't safely do that in this case. This is because the prices are floating point numbers in the question asker's example, but the comparison function we pass to usort has to return integers for usort to work properly:

> Returning non-integer values from the comparison function, such as float, will result in an internal cast to integer of the callback's return value. So values such as 0.99 and 0.1 will both be cast to an integer value of 0, which will compare such values as equal.

This is an important trap to bear in mind when using usort in PHP 5.x! My original version of this answer made this mistake and yet I accrued ten upvotes over thousands of views apparently without anybody noticing the serious bug. The ease with which lackwits like me can screw up comparator functions is precisely the reason that the easier-to-use spaceship operator was added to the language in PHP 7.

While others have correctly suggested the use of array_multisort(), for some reason no answer seems to acknowledge the existence of array_column(), which can greatly simplify the solution. So my suggestion would be:

array_multisort(array_column($inventory, 'price'), SORT_DESC, $inventory);

If you want Case Insensitive Sort on strings, you can use SORT_NATURAL|SORT_FLAG_CASE

array_multisort(array_column($inventory, 'key_name'), SORT_DESC, SORT_NATURAL|SORT_FLAG_CASE, $inventory);

Since your array elements are arrays themselves with string keys, your best bet is to define a custom comparison function. It's pretty quick and easy to do. Try this:

function invenDescSort($item1,$item2)
{
	if ($item1['price'] == $item2['price']) return 0;
	return ($item1['price'] < $item2['price']) ? 1 : -1;
}
usort($inventory,'invenDescSort');
print_r($inventory);

Produces the following:

Array
(
    [0] => Array
        (
            [type] => pork
            [price] => 5.43
        )

    [1] => Array
        (
            [type] => fruit
            [price] => 3.5
        )

    [2] => Array
        (
            [type] => milk
            [price] => 2.9
        )

)

I ended on this:

function sort_array_of_array(&$array, $subfield)
{
	$sortarray = array();
	foreach ($array as $key => $row)
	{
	    $sortarray[$key] = $row[$subfield];
	}
	
	array_multisort($sortarray, SORT_ASC, $array);
}

Just call the function, passing the array and the name of the field of the second level array. Like:

sort_array_of_array($inventory, 'price');

You can use usort with anonymous function, e.g.

usort($inventory, function ($a, $b) { return strnatcmp($a['price'], $b['price']); });

From Sort an array of associative arrays by value of given key in php:

by using usort (http://php.net/usort) , we can sort an array in ascending and descending order. just we need to create a function and pass it as parameter in usort. As per below example used greater than for ascending order if we passed less than condition then it's sort in descending order. Example :

$array = array(
  array('price'=>'1000.50','product'=>'test1'),
  array('price'=>'8800.50','product'=>'test2'),
  array('price'=>'200.0','product'=>'test3')
);

function cmp($a, $b) {
  return $a['price'] > $b['price'];
}

usort($array, "cmp");
print_r($array);

Output:

Array
 (
	[0] => Array
		(
			[price] => 200.0
			[product] => test3
		)

	[1] => Array
		(
			[price] => 1000.50
			[product] => test1
		)

	[2] => Array
		(
			[price] => 8800.50
			[product] => test2
		)
  )

$inventory = 
    array(array("type"=>"fruit", "price"=>3.50),
          array("type"=>"milk", "price"=>2.90),
          array("type"=>"pork", "price"=>5.43),
          );

function pricesort($a, $b) {
  $a = $a['price'];
  $b = $b['price'];
  if ($a == $b)
    return 0;
  return ($a > $b) ? -1 : 1;
}

usort($inventory, "pricesort");
// uksort($inventory, "pricesort");

print("first: ".$inventory[0]['type']."\n\n");
// for usort(): prints milk (item with lowest price)
// for uksort(): prints fruit (item with key 0 in the original $inventory)

// foreach prints the same for usort and uksort.
foreach($inventory as $i){
  print($i['type'].": ".$i['price']."\n");
}

outputs:

first: pork

pork: 5.43
fruit: 3.5
milk: 2.9

For PHP 7 and later versions.

/**
 * A method for sorting associative arrays by a key and a direction.
 * Direction can be ASC or DESC.
 *
 * @param $array
 * @param $key
 * @param $direction
 * @return mixed $array
 */
function sortAssociativeArrayByKey($array, $key, $direction){

    switch ($direction){
        case "ASC":
            usort($array, function ($first, $second) use ($key) {
                return $first[$key] <=> $second[$key];
            });
            break;
        case "DESC":
            usort($array, function ($first, $second) use ($key) {
                return $second[$key] <=> $first[$key];
            });
            break;
        default:
            break;
    }

    return $array;
}

Usage:

$inventory = sortAssociativeArrayByKey($inventory, "price", "ASC");

I use uasort like this

<?php
$users = [
    [
        'username' => 'joe',
        'age' => 11
    ],
    [
        'username' => 'rakoto',
        'age' => 21
    ],
    [
        'username' => 'rabe',
        'age' => 17
    ],
    [
        'username' => 'fy',
        'age' => 19
    ],    
];


uasort($users, function ($item, $compare) {
    return $item['username'] >= $compare['username']; 
});

var_dump($users);

Was tested on 100 000 records: Time in seconds(calculated by funciton microtime). Only for unique values on sorting key positions.

Solution of function of @Josh Davis: Spended time: 1.5768740177155

Mine solution: Spended time: 0.094044923782349

Solution:

function SortByKeyValue($data, $sortKey, $sort_flags=SORT_ASC)
{
	if (empty($data) or empty($sortKey)) return $data;
	
	$ordered = array();
	foreach ($data as $key => $value)
		$ordered[$value[$sortKey]] = $value;
	
	ksort($ordered, $sort_flags);
		
	return array_values($ordered); *// array_values() added for identical result with multisort*
}

try this:

$prices = array_column($inventory, 'price');
array_multisort($prices, SORT_DESC, $inventory);
print_r($inventory);

This function is re-usable:

function usortarr(&$array, $key, $callback = 'strnatcasecmp') {
    uasort($array, function($a, $b) use($key, $callback) {
        return call_user_func($callback, $a[$key], $b[$key]);
    });
}

It works well on string values by default, but you'll have to sub the callback for a number comparison function if all your values are numbers.

You might try to define your own comparison function and then use usort.

Here is a method that I found long ago and cleaned up a bit. This works great, and can be quickly changed to accept objects as well.

/**
 * A method for sorting arrays by a certain key:value.
 * SortByKey is the key you wish to sort by
 * Direction can be ASC or DESC.
 *
 * @param $array
 * @param $sortByKey
 * @param $sortDirection
 * @return array
 */
private function sortArray($array, $sortByKey, $sortDirection) {

    $sortArray = array();
    $tempArray = array();

    foreach ( $array as $key => $value ) {
        $tempArray[] = strtolower( $value[ $sortByKey ] );
    }

    if($sortDirection=='ASC'){ asort($tempArray ); }
        else{ arsort($tempArray ); }

    foreach ( $tempArray as $key => $temp ){
        $sortArray[] = $array[ $key ];
    }

    return $sortArray;

}

to change the method to sort objects simply change the following line:

$tempArray[] = strtolower( $value[ $sortByKey ] ); to $tempArray[] = strtolower( $value->$sortByKey );

To run the method simply do

sortArray($inventory,'price','ASC');

//Just in one line custom function
function cmp($a, $b)
{
return (float) $a['price'] < (float)$b['price'];
}
@uasort($inventory, "cmp");
print_r($inventory);

//result

Array
(
[2] => Array
    (
        [type] => pork
        [price] => 5.43
    )

[0] => Array
    (
        [type] => fruit
        [price] => 3.5
    )

[1] => Array
    (
        [type] => milk
        [price] => 2.9
    )

)

As of PHP 7.4, you can use arrow function:

usort(
    $inventory, 
    fn(array $a, array $b): int => $b['price'] <=> $a['price']
);

Code (demo):

$inventory = [
    ['type' => 'fruit', 'price' => 3.50],
    ['type' => 'milk',  'price' => 2.90],
    ['type' => 'pork',  'price' => 5.43],
];

usort(
    $inventory, 
    fn(array $a, array $b): int => $b['price'] <=> $a['price']
);

print_r($inventory);

(condensed) Output:

Array
(
    [0] => Array ([type] => pork,  [price] => 5.43)
    [1] => Array ([type] => fruit, [price] => 3.5)
    [2] => Array ([type] => milk,  [price] => 2.9)
)

Complete Dynamic Function I jumped here for associative array sorting and found this amazing function on http://php.net/manual/en/function.sort.php. This function is very dynamic that sort in ascending and descending order with specified key.

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

<?php

function array_sort($array, $on, $order=SORT_ASC)
{
    $new_array = array();
    $sortable_array = array();

    if (count($array) > 0) {
        foreach ($array as $k => $v) {
            if (is_array($v)) {
                foreach ($v as $k2 => $v2) {
                    if ($k2 == $on) {
                        $sortable_array[$k] = $v2;
                    }
                }
            } else {
                $sortable_array[$k] = $v;
            }
        }

        switch ($order) {
            case SORT_ASC:
                asort($sortable_array);
            break;
            case SORT_DESC:
                arsort($sortable_array);
            break;
        }

        foreach ($sortable_array as $k => $v) {
            $new_array[$k] = $array[$k];
        }
    }

    return $new_array;
}

$people = array(
    12345 => array(
        'id' => 12345,
        'first_name' => 'Joe',
        'surname' => 'Bloggs',
        'age' => 23,
        'sex' => 'm'
    ),
    12346 => array(
        'id' => 12346,
        'first_name' => 'Adam',
        'surname' => 'Smith',
        'age' => 18,
        'sex' => 'm'
    ),
    12347 => array(
        'id' => 12347,
        'first_name' => 'Amy',
        'surname' => 'Jones',
        'age' => 21,
        'sex' => 'f'
    )
);

print_r(array_sort($people, 'age', SORT_DESC)); // Sort by oldest first
print_r(array_sort($people, 'surname', SORT_ASC)); // Sort by surname

If you need to sort an array of strings with different cases, this will change the sorting array values to lowercase.

$data = [
    [
        'name' => 'jack',
        'eyeColor' => 'green'
    ],
    [
        'name' => 'Amy',
        'eyeColor' => 'brown'
    ],
    [   
        'name' => 'Cody',
        'eyeColor' => 'blue'
    ] 
];
function toLowerCase($a) { return strtolower($a); }
$sortArray = array_map("toLowerCase",array_column($data, 'name'));
array_multisort($sortArray, SORT_ASC, $data);

This function works 100% on all major versions of PHP and it is tested with PHP5, PHP7, PHP8.

    function sort_my_array($array, $order_by, $order)
    {
        switch ($order) {
            case "asc":
                usort($array, function ($first, $second) use ($order_by) {
                    if (version_compare(PHP_VERSION, '7.0.0') >= 0) {
                        return $first[$order_by] <=> $second[$order_by];
                    } else {
                        $array_cmp = strcmp($first[$order_by], $second[$order_by]);
                        return $array_cmp ;
                    }
                });
                break;
            case "desc":
                usort($certificates, function ($first, $second) use ($order_by) {
                    if (version_compare(PHP_VERSION, '7.0.0') >= 0) {
                        return $first[$order_by] <=> $second[$order_by];
                    } else {
                        $array_cmp = strcmp($first[$order_by], $second[$order_by]);
                        return -$array_cmp ;
                    }
                });
                break;
            default:
                break;
        }
        return $array;
    }

$arr1 = array(

    array('id'=>1,'name'=>'aA','cat'=>'cc'),
    array('id'=>2,'name'=>'aa','cat'=>'dd'),
    array('id'=>3,'name'=>'bb','cat'=>'cc'),
    array('id'=>4,'name'=>'bb','cat'=>'dd')
);

$result1 = array_msort($arr1, array('name'=>SORT_DESC);

$result2 = array_msort($arr1, array('cat'=>SORT_ASC);

$result3 = array_msort($arr1, array('name'=>SORT_DESC, 'cat'=>SORT_ASC));


function array_msort($array, $cols)
{
    $colarr = array();
    foreach ($cols as $col => $order) {
    $colarr[$col] = array();
    foreach ($array as $k => $row) { $colarr[$col]['_'.$k] = strtolower($row[$col]); }
}

$eval = 'array_multisort(';

foreach ($cols as $col => $order) {
    $eval .= '$colarr[\''.$col.'\'],'.$order.',';
}

$eval = substr($eval,0,-1).');';
eval($eval);
$ret = array();
foreach ($colarr as $col => $arr) {
    foreach ($arr as $k => $v) {
        $k = substr($k,1);
        if (!isset($ret[$k])) $ret[$k] = $array[$k];
        $ret[$k][$col] = $array[$k][$col];
    }
}
return $ret;


} 

try this:

asort($array_to_sort, SORT_NUMERIC);

for reference see this: http://php.net/manual/en/function.asort.php

see various sort flags here: http://www.php.net/manual/en/function.sort.php