How to sort and group datas in a php array where some datas are repeated?

Question

I have a php array which contains sometimes same values (in my example film 1 and film 2) and i would like to sort the result in order to keep only one time film 1 or film 2.

PHP array : $actors

Array
(
    [0] => Array
        (
            [0] => film 1
            [1] => actor A
        )

    [1] => Array
        (
            [0] => film 1
            [1] => actor B
        )

    [2] => Array
        (
            [0] => film 2
            [1] => actor C
        )

    [3] => Array
        (
            [0] => film 2
            [1] => actor D
        )
)

I can output the datas in a foreach loop :

$i = 0;
foreach ($films as $film):

    echo $film[$i][0].'<br />';
    echo $film[$i][1];

    $i ++;

endforeach;

And i get a result like this :

 film1 actor A film1 actor B film2 actor C film2 actor D 

But i would like to have a result like this :

film 1
actor A
actor B

film 2
actor C
actor E

What i've done :

I made an array with films : $films

Array
(
    [0] => stdClass Object
        (
            [name] => film1
        )

    [1] => stdClass Object
        (
            [name] => film2
        )

And i check if datas in $films array exist in actors array :

$i = 0;
foreach ($films as $film):

    foreach ($actors as $actor):

    if ($film->name == $actor[$i][0]) {

        echo $actor[$i][1].'<br />';
    }

    endforeach;

    $i ++;

endforeach;

So this code works for me but is there a better solution ? In my solution, i have a foreach loop inside a foreach loop and it could consume a lot of ressources.

Answer 1

For what you're looking to do, there's not a lot you can do to avoid the looping, but you could structure your array a little bit to make it do what you want. Instead of having two separate arrays of $films and $actors , you would want to create one array of $films and each $actors array is associated with the film:

$films = []; // PHP 5.4 style array shortcut. Creates a new empty array (same as array())

foreach($actors as $actor)
{
    $filmName = $actor[0];
    $actorName = $actor[1];

    // If this film isn't in the array yet, let's create it
    if(!isset($films[$filmName])) 
    {
        $films[$filmName] = []; 
    }

    // Add the actor to the film array
    array_push($films[$filmName], $actorName);
}

Running the above code on your $actors array results in the following $films array

Array
(
    [film 1] => Array
        (
            [0] => actor A
            [1] => actor B
        )

    [film 2] => Array
        (
            [0] => actor C
            [1] => actor D
        )

)

To gain access to the list of actors in a film, you can just use $films["film 1"] and it'll give you the array of actors.