Display some widgets from a sidebar in random order

gistfile1.aw

<?php

add_filter( 'sidebars_widgets', 'gmj_shuffle_widgets' );
/**
 * Shuffle ranges of widgets within a sidebar.
 *
 * Hat-tip to {@link http://gmj.to/op} for the original idea.
 *
 * @uses gmj_do_shuffle_widgets() Does the actual array manipulation.
 *
 * @param  array $sidebar_widgets Associative array of all sidebars and their widgets.
 * @return array                  Amended array of all sidebars and their widgets.
 */
function gmj_shuffle_widgets ( array $sidebars_widgets ) {

	// Only affect the front-end ordering
	if ( is_admin() )
		return $sidebars_widgets;
	
	// Shuffle 2nd, 3rd and 4th widgets within the sidebar 'sidebar'
	$sidebars_widgets = gmj_do_shuffle_widgets( $sidebars_widgets, 'sidebar', 2, 4 );
	
	// Shuffle 5th and 6th widgets within the sidebar 'sidebar'
	$sidebars_widgets = gmj_do_shuffle_widgets( $sidebars_widgets, 'sidebar', 5, 6 );
	
	// Shuffle 1st, 2nd, 3rd, 4th and 5th widgets within the sidebar 'sidebar-alt'
	$sidebars_widgets = gmj_do_shuffle_widgets( $sidebars_widgets, 'sidebar-alt', 1, 5 );
		
	return $sidebars_widgets;
	
}

/**
 * Shuffle a range of widgets in a sidebar.
 *
 * Could be generalised to shuffle a consecutive range of items in an array.
 *
 * @param  array   $sidebar_widgets Associative array of all sidebars and their widgets.
 * @param  string  $sidebar         The ID of the sidebar.
 * @param  integer $random_start    The first widget to include in the shuffle.
 * @param  integer $random_end      The last widget to include in the shuffle.
 * @return array                    Amended array of all sidebars and their widgets.
 */
function gmj_do_shuffle_widgets( array $sidebars_widgets, $sidebar, $start, $end ) {
	
	// Group into before, shufflable and after widgets
	$head = array_slice( $sidebars_widgets[$sidebar], 0, $start - 1 );
	$body = array_slice( $sidebars_widgets[$sidebar], $start - 1, $end - $start + 1 );
	$tail = array_slice( $sidebars_widgets[$sidebar], $end );
	
	// Mix those bad boys up
	shuffle( $body );

	// Put all the parts back together again
	$sidebars_widgets[$sidebar] = array_merge( $head, $body, $tail );

	// Send Humpty Dumpty back on his way
	return $sidebars_widgets;
	
}

This is working great!
I was getting some error messages before I used the appropriate sidebar id. Duh!