wp_randomize_widgets-function.php

/** 
 * Randomize widgets in a given sidebar (index) and only display a single widget
 * 
 * @See http://wordpress.stackexchange.com/a/152408/26350 
 * 
 * Good for Ad banners (simple)
 *
 */
! is_admin() && add_filter( 'sidebars_widgets', function( $sidebars_widgets ) {
    // ------------------------
    // Edit this to your needs:
    $sidebar_index = 'top_header';
    // ------------------------
    if( isset( $sidebars_widgets[$sidebar_index] ) )
    {
         // Randomize the array:
         shuffle( $sidebars_widgets[$sidebar_index] );
         // Slice the array:
         $sidebars_widgets[$sidebar_index] = array_slice( $sidebars_widgets[$sidebar_index], 0, 1 );
    }
    return $sidebars_widgets;
}, PHP_INT_MAX );
//SAME FUNCTION
! is_admin() && add_filter( 'sidebars_widgets', function( $sidebars_widgets2 ) {
    // ------------------------
    // Edit this to your needs:
    $sidebar_index2 = 'footerfull';
    // ------------------------
    if( isset( $sidebars_widgets2[$sidebar_index2] ) )
    {
         // Randomize the array:
         shuffle( $sidebars_widgets2[$sidebar_index2] );
         // Slice the array:
         $sidebars_widgets2[$sidebar_index2] = array_slice( $sidebars_widgets2[$sidebar_index2], 0, 1 );
    }
    return $sidebars_widgets2;
}, PHP_INT_MAX );