Could anyone advise me on the most simple and efficient way of getting 'keys' out of a multi-dimensional array.

I have the multi-dimensional Array :

PHP Code:
This array stores the relationships between $C[] , $L[] & $P[] as Keys, which I then want to use in individual queries. Rather than having to use 3 loops to get the inforamtion (I want to get all the keys for each sub-array) is there not an easier more efficient function I could use ?? I tried the below but it through out errors as I can't use [] for reading.

PHP Code:
    $C_QUERY_ids array_keys($C_L_P_CurrentPage);
$L_QUERY_ids array_keys($C_L_P_CurrentPage[]);
$P_QUERY_ids array_keys($C_L_P_CurrentPage[][]);); 
Many Thanks