return all keys of a associative array with a function

Question

I have an associative array which looks like this:

Array ( 
[0] => Array ( ) 
[1] => Array ( ) 
[2] => Array ( [318] => 3.3333333333333 ) 
[3] => Array ( ) 
[4] => Array ( ) 
[5] => Array ( [317] => 5 ) 
)

I want to return all the array keys of the array as number, not string; thats why I am not echoing it. This is how I am trying:

function user_rated_posts(){
    global $author;

if(isset($_GET['author_name'])) :
$curauth = get_userdatabylogin($author_name);
else :
$curauth = get_userdata(intval($author));
endif;

$user_rated_posts = get_user_meta($curauth->ID, 'plgn_rating',true); 
foreach ($user_rated_posts as $arrs){
    foreach($arrs as $key=> $value){
        $keys= $key;
        }
    }
return $keys;
}

when I call the function like this:

array( explode(',',user_rated_posts()) )

I am only getting this

array(317)

I am trying to get all the keys in comma separated format, like:

array(318, 317)

Thanks.

Answer 1

You're overwriting the $keys variable each time you go through your loop, so it's always only set to the last one.

$keys = array();
foreach ($user_rated_posts as $arrs) {
    foreach($arrs as $key=> $value){
        $keys[] = $key;
    }
}
return $keys;

... that will return an actual array structure, if you actually want a comma separated list then return implode(', ', $keys); instead.

Answer 2

You could use array_keys($array) instead of looping twice.

$keys = array();
foreach ($user_rated_posts as $arrs) {
    $keys = array_merge($keys, array_keys($array));
}
return $keys;

Answer 3

I came up with a way that avoids the nested looping in favor of PHP's built in functions:

$result = array_map(array_keys,$user_rated_posts);
$result2 = array_map(implode, $result);
$result3 = array_filter($result2);

First line iterates over the array, returning the keys. Second line reduces the sub-array to strings. Third line removes the empty values.

Here is a working version: https://eval.in/99119

Added bonus: keeps the positions where the values were found as the keys like:

array(2) {
  [2]=>
  string(3) "318"
  [5]=>
  string(3) "317"
}