Loop over Array and get the distinct ids

Question

I've made a loop that goes over all the gigs I've attended, some gigs have the same songs.

Here is the result of that array: http://snippi.com/s/k80v7pe

Now I want to have an array of all the distinct song id's. So want to see all the songs that I've ever heard:

//get the songs field get_field('songs')
foreach ($postIds as $postId){ 
    array_push($songIds, get_field('songs', $postId));  
} 

//Over here I'm trying to print all the ID's of the song
foreach ($songIds as $songId) {
    echo $songId->ID;
}

But I'm getting the following error:

Notice: Trying to get property 'ID' of non-object in

Is that because of that the array $songIds has an array in an array?

Answer 1

No, that's because you are treating an array as an object and PHP doesn't convert those types automatically. To get an individual element from an object you use:

$my_object->Element1;

To get an individual element from an array you use:

$my_array[Element1];

You can even nest arrays. So if you have $my_array, where each element is another array, you can get elementX from arrayY like this:

$my_array[arrayY][elementX];

In your case, apparently, you have an array, which holds an array, which holds objects, amounting to:

$my_array[arrayY][elementX]->componentZ

Answer 2

Because $songIds is an array within an array, I have to do 2 loops within each other.

The code below pushes all post id's from the different arrays in a new array $allSongs.

This way I have an array with all the id's. Some id's will be duplicates because some songs are played more than 1 time over all the gigs.

foreach ($songIds as $songId) {
    foreach ($songId as $key => $value) {
        array_push($allSongs, $value->ID);
    }
}

//all songs
print_r($allSongs);

To retrieve only unique id's, you can use the array function array_unique to remove the duplicates from an array.

$uniqueSongs = array_unique($allSongs, SORT_REGULAR);
print_r($uniqueSongs);