Help with Loop through PDO objects and buildings associative arrays

$item is an array that contains details about the media item. $results is a PDOstatement object with our genre results. Loop through the $results and add an additional "genres" element to $item. This "genres" element should have an internal associative array with the key of genre_id and the value of genre. Example $item array: array(8) { ... ["genres"]=> array(2) { [3]=> string(6) "Comedy" [16]=> string(6) "Sci-Fi" } }

i don't understand how do that, i try to do this:

while($row = $results->fetch(PDO::FETCH_ASSOC)) { $item[$row["genres"]][] = $row["genre_id"=>"genre"]; }

but i know in the $row[''genre_id... has a sintax error, someone can help me?

<?php

include "helper.php";

/*
 * helper contains the following variables:
 * $item is an array that contains details about the library item
 * $results is a PDOstatement object with our genre results.
 */