Show only free shipping option in WooCommerce when available

/**
* Show only free shipping option when available
*
* @param array $available_methods
*/
function show_only_free_shipping( $available_methods ) {
 
  	if( isset( $available_methods['free_shipping'] ) ) :
		
		// Get Free Shipping array into a new array
		$freeshipping = array();
		$freeshipping = $available_methods['free_shipping'];
 
		// Empty the $available_methods array
		unset( $available_methods );
 
		// Add Free Shipping back into $available_methods
		$available_methods = array();
		$available_methods[] = $freeshipping;
 
	endif;
 
	return $available_methods;
}
add_filter( 'woocommerce_available_shipping_methods', 'show_only_free_shipping' , 10, 1 );