Search results in random order

Do you want to order your search results in random order? Here’s how:

add_filter( 'relevanssi_hits_filter', 'shuffle_search' );
function shuffle_search( $hits ) {
    shuffle( $hits[0] );
    return $hits;
}

Add this function to your site and the search results will appear in random order. You can also do this:

add_filter( 'relevanssi_modify_wp_query', function ( $query ) {
  $query->set( 'orderby', 'rand' );
  return $query;
}

However, both of these solutions only work if all the search results are on the same page. If the results span multiple pages, they will be shuffled between page switches, and the second page can have results from the first page on it, and some posts may never appear in results.

Here’s a more complicated solution that solves the issue by setting the random number generator seed every hour. Searches within that hour will return the results in the same order. This means pagination will work (unless the searcher loads the first page on 00:59 and the second page on 01:00, in which case the results come from a different set).

add_filter( 'relevanssi_hits_filter', 'shuffle_search' );
function shuffle_search( $hits ) {
    $date = date( 'Ymdh' );
    seeded_shuffle( $hits[0], $date );
    return $hits;
}

function seeded_shuffle( &$items, $string ) {
    mt_srand( strlen( $string ) ); 
    for ( $i = count( $items ) - 1; $i > 0; $i-- ) { 
        $j           = @mt_rand( 0, $i ); 
        $tmp         = $items[ $i ]; 
        $items[ $i ] = $items[ $j ]; 
        $items[ $j ] = $tmp; 
    } 
}

The seeded shuffle function is from PHP documentation.