How to break meta values into different items and avoid duplicates?

This is just a basic php array question – not a WP question.

function unique_authors ( $authors ) {
    $newArray = array();

    foreach( $authors as $item ) {
        $itemArray = explode( ", ", $item );
        $newArray = array_merge($newArray, $itemArray);
    }

    $newArray = array_unique($newArray);
    return $newArray;
}

$authors = unique_authors( $authors );

foreach( $authors as $author ):  //etc