Best Way To Sort Multidimensional Array in PHP

Question

I have this array :

$order_list = array ( array ("081", "01203", "2", "12000"),
                      array ("002", "01204", "8", NULL),
                      array ("021", "01207", "8", NULL),
                      array ("081", "01206", "8", NULL),
                      array ("043", "01205", "10", "14000"));

and I want to sort (ascending) that array based on the first value (081, 002, 021, 081 and 043). so it will look like this :

array ( array ("002", "01204", "8", NULL),
        array ("021", "01207", "8", NULL),
        array ("043", "01205", "10", "14000"),
        array ("081", "01203", "2", "12000"),
        array ("081", "01206", "8", NULL));

how to do that? I learned about asort() and ksort(), but it seems that only works for associative array, not multidimensional array.

Look over at the Related column on the 'right hand side' of this page... There are a lot of very useful questions and answers. Also, search Google: php sort multi array . — Ryan Vincent
– Ryan Vincent, Commented Jan 22, 2016 at 11:07
this is such a duplicate question (and any answers) :) It has to one of the most popular questions here. — Ryan Vincent
– Ryan Vincent, Commented Jan 22, 2016 at 11:10

Michael · Accepted Answer · 2016-01-22 10:59:54Z

3

You can use usort()

usort($yourArray, function ($a, $b) {
    if ($a[0] == $b[0]) return 0;
    return (int) $a[0] < (int) $b[0] ? -1 : 1;
});

The parameters $a and $b are your (sub)arrays. This simple function compares the first value in each of those.

If you had other than numbers in your array you could have used strcmp():

usort($yourArray, function ($a, $b) {
    return strcmp($a[0], $b[0]);
});

answered Jan 22, 2016 at 10:59

Michael

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9 Comments

morido Over a year ago

Be aware that usort exhibits undefined behavior (first Note in that link) if your sorting function returns 0.

Michael Over a year ago

@morido, you make it seem worse than it is. It simply states that there is no way of telling if there value 0 is returned then usort cannot tell which of the two (arrays in this case) comes first, which is perfectly fine, since there are deemed to be equal.

morido Over a year ago

I am just saying how it is. After all, it's a beautiful source of (hard to find) bugs. So I prefer to always make the behavior deterministic and either force $a or $b to be sorted in first, rather than to leave this to the implementation.

Michael Over a year ago

@morido so what would be the "correct" way to determine -1 or 1 for two arrays that are identical?

morido Over a year ago

Well the point is, that PHP does not make any statements about the order of equal elements. This is different to other languages, where such operations often guarantee stability (i.e. predictable behavior) in such situations. See for instance Arrays.sort in Java.

|

Ihor Burlachenko · Accepted Answer · 2016-01-22 11:09:02Z

1

It is easier to rewrite this way:

usort($order_list, function($v1, $v2) { return $v1[0] - $v2[0]; });

Or it is very convenient to sort arrays with sorted function from Nspl:

use function \nspl\a\sorted;
use function \nspl\op\itemGetter;

$sortedOrders = sorted($order_list, itemGetter(0));

edited Jan 22, 2016 at 11:09

answered Jan 22, 2016 at 11:03

Ihor Burlachenko

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3 Comments

Michael Over a year ago

Nice touch with the return $a - $b

Michael Over a year ago

I just tried what would happen if you omitted the cast part (int) that works fine as well. So you can just do return $v1[0] - $v2[0];

Ihor Burlachenko Over a year ago

Nice finding. Since - is not defined for string PHP is casting values to numeric automatically. Updating the answer.

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