Individually sorting subarrays of an array

Question

I have an array of numeric subarrays. I want to sort all the subarrays, and then sort the whole array, and remove duplicates. Using sort($val) doesn't work, so I found the following workaround with $derp, which I find insanely stupid:

$arr = array( array(5,6), array(1,2), array(6,5) );
foreach ($arr as $key => $val) {
    $derp = $val;
    sort($derp);
    $arr[$key] = $derp;
}
sort($arr);
$arr = array_map("unserialize", array_unique(array_map("serialize", $arr)));

The result is array( array(1,2), array(5,6) ). Is that is the correct way to do this in PHP, or is there a better and shorter way?

I created a pastebin as a response to the first answer: pastebin.com/Y5vNvKKL
This question is not anymore just about a less goofy way to write this: Now the question is:
Why does sort() in array_work() not give the same result as sort() in foreach?

By the way: This is about finding the partitions of multisets.

hakre · Accepted Answer · 2025-02-03 05:35:45Z

1

I'd approach it like this:

array_walk($arr, fn (&$value) => sort($value));

$deduped = array();
foreach ($arr as $val) {
    $deduped[serialize($val)] = $val;
}

$arr = array_values($deduped);

edited Feb 3 at 5:35

hakre

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answered Nov 3, 2014 at 11:47

deceze♦

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5 Comments

Watchduck Over a year ago

array_walk() was what I was looking for, thanks. BTW, your code gives array( array(5,6), array(1,2) ).

Watchduck Over a year ago

Actually this doesn't always work in the same way as the $derp version. This may have to do with the fact, that my array contains not only arrays, but also single numbers. See pastebin.com/Y5vNvKKL

Watchduck Over a year ago

I mean: This may have to do with the fact, that the subarray contain not only single numbers, but also arrays. However, it is weird, because the code suggests that we do the same in both cases: Apply sort() to all subarrays. But the result is not the same.

mickmackusa Jan 28 at 23:50

array_walk($array, 'sort') must not be recommended for general-use because the keys parameter in the callback of array_walk will funk with sorts second parameter. Proof can be seen in keyed rows 2, 5, 10, and 13 here: 3v4l.org/Yn9mc

mickmackusa Feb 2 at 23:20

Why should native sorting functions be called by array_walk() with explicit sorting function parameters?

mickmackusa · Accepted Answer · 2025-01-28 12:21:44Z

0

array_unique($array, SORT_REGULAR) is quite convenient for filtering whole rows of a 2d array, but it respects associative relationships when checking for uniqueness. Demo

$array = [[5, 6], [1, 2], [6, 5], [1, 2], [1 => 2, 0 => 1]];

var_export(
    array_unique($array, SORT_REGULAR)
);

Output: [[5, 6], [1, 2], [6, 5]]

Feed sorted rows to that technique and everything works out as expected. Demo

var_export(
    array_unique(
        array_map(
            function ($row) {
                sort($row);
                return $row;
            },
            $array
        ),
        SORT_REGULAR
    )
);

Output: [[5, 6], [1, 2]]

answered Jan 28 at 12:21

mickmackusa♦

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