CODEWITHSUNDEEP
phpasort
hsz
hsz

Reputation: 152266

PHP's asort does not work properly?

I have an example array:

$a = array(
    5   => 35,
    16  => 22,
    7   => 22,
    3   => 22,
    11  => 22,
    9   => 27,
);

and I want to sort it by values and remember its keys. Result that I expected was:

$a = array(
    16  => 22,
    7   => 22,
    3   => 22,
    11  => 22,
    9   => 27,
    5   => 35,
);

So my first thought was: asort ! Ok, I did

asort($a);

But no - it didn't just move 5 => 35 to the end of the array. It changed my array to:

$a = array(
    11  => 22,
    3   => 22,
    7   => 22,
    16  => 22,
    9   => 27,
    5   => 35
);

You see ? Keys with the same value are reverse sorted. Why ?

Upvotes: 3

Views: 3797

Answers (3)

Pekka
Pekka

Reputation: 449613

It depends on whether a sorting algorithm is stable or not. For a stable sort, upgrade your PHP version. PHP manual on Sorting Arrays:

If any of these sort functions evaluates two members as equal then they retain their original order. Prior to PHP 8.0.0, their order were undefined (the sorting was not stable).

Upvotes: 12

badideas
badideas

Reputation: 3567

http://en.wikipedia.org/wiki/Sorting_algorithm#Stability

in short, making sure that the order of the already sorted keys remains the same would cost computation time (and whoever designed the function at PHP decided it wasn't worth it)

Upvotes: 3

aularon
aularon

Reputation: 11110

Depending on the sort algorithm, it probably started sorting in another manner than just detecting that it should only move that single pair. But it ended up with a validly sorted array maintaining keys/values. they only look swapped cuz you have 4 keys with values of 22.

Upvotes: 1

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