Combine multiple queries, array_unique returns nothing

Question

I'm combining multiple queries for a loop using the following method:

function order_by_date( $a, $b )
{
    return strcmp( $b->post_date, $a->post_date );
}
// get the posts for the first query
$q1_args = array(
    // args for the first query 
);
$q1_posts = get_posts( $q1_args );
// get the posts for the second query
$q2_args = array(
    // args for the second query
);
$q2_posts= get_posts( $q2_args );
// Merge the post arrays together, and sort by date using the order_by_date function
$final_posts = array_merge( $q1_posts, $q2_posts );

usort( $final_posts, 'order_by_date' );
// Loop over the posts and use setup_postdata to format for template tag usage
foreach ( $final_posts as $key => $post ) {
    setup_postdata( $post ); 
    // Now we can use template tags as if this was in a normal WP loop
    the_title('<h2>','</h2>');
    the_content();
}

This works fine, but when I try to remove duplicates, I get nothing (no errors either):

// This is my code for trying to remove the duplicates
$final_posts = array_unique( array_merge( $q1_posts, $q2_posts ) );

Any ideas on what could be going wrong?

Answer 1

It will work with the SORT_REGULAR flag:

array_unique( array_merge( $q1_posts, $q2_posts ), SORT_REGULAR );

Answer 2

Thanks to Michael's answer, I used an alternative method:

Before the loop, create an array:

$do_not_duplicate = array(); // set an array for catching duplicates

Then inside the loop, add the post id to the array, and skip over it if it is already in it:

if (in_array($postID, $do_not_duplicate)) {
 continue; // if its already been through it, dont display it
 }
$do_not_duplicate[] = $postID; // add the id to the array