comparing arrays in php, without caring for the or

Question

I have two arrays, $a and $b here, and need to check if they contain exactly the same elements (independently of the order). I am thinking of using

if (sizeof($a)==sizeof($b) AND array_diff($a,$b)==array())
{

}

But I am new to PHP, so I wonder: Is there a better way?

Since I need to use them as sets, maybe I should not use arrays at all but something else.

Answer 1

The accepted answer fails to account for duplicates. Here is my take

public function sameElements($a, $b)
{
   sort($a);
   sort($b);
   return $a == $b;
}

Answer 2

The accepted answer is wrong! It will fail on: https://3v4l.org/U8U5p

$a = ['x' => 1, 'y' => 2]; $b = ['x' => 1, 'y' => 1];

Here is a correct solution:

function consistsOfTheSameValues(array $a, array $b)
{
    // check size of both arrays
    if (count($a) !== count($b)) {
        return false;
    }

    foreach ($b as $key => $bValue) {

        // check that expected value exists in the array
        if (!in_array($bValue, $a, true)) {
            return false;
        }

        // check that expected value occurs the same amount of times in both arrays
        if (count(array_keys($a, $bValue, true)) !== count(array_keys($b, $bValue, true))) {
            return false;
        }

    }

    return true;
}

Plus quite extensive unit tests: https://3v4l.org/m6lHv

<?php

// A unit testing framework in a tweet. https://gist.github.com/mathiasverraes/9046427
function it($m,$p){echo ($p?'✔︎':'✘')." It $m\n"; if(!$p){$GLOBALS['f']=1;}}function done(){if(@$GLOBALS['f'])die(1);}

function consistsOfTheSameValues(array $a, array $b)
{
    // check size of both arrays
    if (count($a) !== count($b)) {
        return false;
    }

    foreach ($b as $key => $bValue) {

        // check that expected value exists in the array
        if (!in_array($bValue, $a, true)) {
            return false;
        }

        // check that expected value occurs the same amount of times in both arrays
        if (count(array_keys($a, $bValue, true)) !== count(array_keys($b, $bValue, true))) {
            return false;
        }

    }

    return true;
}

it('consist of the same values',
    consistsOfTheSameValues([1], [1]) === true
);

it('consist of the same values',
    consistsOfTheSameValues([1, 1], [1, 1]) === true
);

it('consist of the same values',
    consistsOfTheSameValues(['1', 1], ['1', 1]) === true
);

it('consist of the same values',
    consistsOfTheSameValues(['1', 1], [1, '1']) === true
);

it('consist of the same values',
    consistsOfTheSameValues([1, '1'], ['1', 1]) === true
);

it('consist of the same values',
    consistsOfTheSameValues([1, '1'], [1, '1']) === true
);

it('consist of the same values',
    consistsOfTheSameValues(['x' => 1], ['x' => 1]) === true
);

it('consist of the same values',
    consistsOfTheSameValues(['x' => 1], ['y' => 1]) === true
);

it('consist of the same values',
    consistsOfTheSameValues(['y' => 1], ['x' => 1]) === true
);

it('consist of the same values',
    consistsOfTheSameValues(['x' => 1, 'y' => 1], ['x' => 1, 'y' => 1]) === true
);

it('consist of the same values',
    consistsOfTheSameValues(['y' => 1, 'x' => 1], ['x' => 1, 'y' => 1]) === true
);

it('consist of the same values',
    consistsOfTheSameValues(['x' => 1, 'y' => 1], ['y' => 1, 'x' => 1]) === true
);

it('consist of the same values',
    consistsOfTheSameValues(['y' => 1, 'x' => 1], ['y' => 1, 'x' => 1]) === true
);

it('consist of the same values',
    consistsOfTheSameValues(['x' => 2, 'y' => 1], ['x' => 1, 'y' => 2]) === true
);

it('does not consist of the same values',
    consistsOfTheSameValues([1], [2]) === false
);

it('does not consist of the same values',
    consistsOfTheSameValues(['1'], [1]) === false
);

it('does not consist of the same values',
    consistsOfTheSameValues([1], ['1']) === false
);

it('does not consist of the same values',
    consistsOfTheSameValues([1], [1, 1]) === false
);

it('does not consist of the same values',
    consistsOfTheSameValues([1, 1], [1]) === false
);

it('does not consist of the same values',
    consistsOfTheSameValues(['1', 1], [1, 1]) === false
);

it('does not consist of the same values',
    consistsOfTheSameValues([1, '1'], [1, 1]) === false
);

it('does not consist of the same values',
    consistsOfTheSameValues([1, 1], ['1', 1]) === false
);

it('does not consist of the same values',
    consistsOfTheSameValues([1, 1], [1, '1']) === false
);

it('does not consist of the same values',
    consistsOfTheSameValues(['1', '1'], [1, 1]) === false
);

it('does not consist of the same values',
    consistsOfTheSameValues(['1', '1'], ['1', 1]) === false
);

it('does not consist of the same values',
    consistsOfTheSameValues(['1', '1'], [1, '1']) === false
);

it('does not consist of the same values',
    consistsOfTheSameValues([1, 1], ['1', '1']) === false
);

it('does not consist of the same values',
    consistsOfTheSameValues(['1', 1], ['1', '1']) === false
);

it('does not consist of the same values',
    consistsOfTheSameValues([1, '1'], ['1', '1']) === false
);

it('does not consist of the same values',
    consistsOfTheSameValues(['x' => 1], ['x' => 2]) === false
);

it('does not consist of the same values',
    consistsOfTheSameValues(['x' => 1, 'y' => 1], ['x' => 1, 'y' => 2]) === false
);

it('does not consist of the same values',
    consistsOfTheSameValues(['x' => 1, 'y' => 1], ['x' => 2, 'y' => 1]) === false
);

it('does not consist of the same values',
    consistsOfTheSameValues(['x' => 2, 'y' => 1], ['x' => 1, 'y' => 1]) === false
);

@update:

Extensive unit test of @ircmaxell answer: https://3v4l.org/5ivgm

Extensive unit test of @Jon anwser: https://3v4l.org/CrTgQ

Answer 3

If you think of the arrays as sets:

Then your approach is almost correct (you need to drop the equality test for the element count).

If it matters that the arrays contain multiple copies of the same element:

Then your approach is not correct. You need to sort the arrays with sort and then compare them with ===. This should be faster, as it can abort the comparison the moment it sees one difference without going over the whole arrays.

Update:

Clarified exactly when the OP's approach would be correct or not, also incorporated the suggestion that sort would be probably better than asort here.

Answer 4

Well, we can do something like this:

if (count(array_diff(array_merge($a, $b), array_intersect($a, $b))) === 0) {
    //they are the same!
}

The reason it works, is that array_merge will make a big array that has all the elements of both $a and $b (all the elements that are in either $a, $b, or both). array_intersect will create an array that has all the elements that are in both $a and $b only. So if they are different,, there must be at least one element that does not appear in both arrays...

Also note that sizeof is not an actual function/construct, it's an alias. I'd suggest using count() for clarity...

Answer 5

Just for your amusement I'll add an example that demonstrates that your conditions is not correct:

<?php
$a = array(1, 1, 2);
$b = array(1, 2, 3);

var_dump(sizeof($a)==sizeof($b) AND array_diff($a,$b)==array());
?>

Test it.

I would suggest using a different model. Maybe adding the elements as keys of the array, but this is possible only if they are integers or strings.

$arr['itemA'] = true;
$arr['itemB'] = true;

This will enforce uniqueness. With this model you can use your condition on array_keys($arr).