Hide other shipping methods except local delivery when “Free Shipping” is available

hide-when-free-avaialble.php

/**
 * Hide shipping rates except local delivery when free shipping is available.
 * Updated to support WooCommerce 2.6 Shipping Zones.
 *
 * @param array $rates Array of rates found for the package.
 * @return array
 */
function my_hide_shipping_when_free_is_available( $rates ) {
	$free = array();
	$local_pickup = array();
	foreach ( $rates as $rate_id => $rate ) {
		if ( 'free_shipping' === $rate->method_id ) {
			$free[ $rate_id ] = $rate;
		}
		elseif ( 'local_pickup' === $rate->method_id ) {
			$local_pickup[ $rate_id ] = $rate;
		}
	}
  	if( !empty( $free ) ) {
		return array_merge( $free, $local_pickup );
  	}
	return $rates;
}
add_filter( 'woocommerce_package_rates', 'my_hide_shipping_when_free_is_available', 100 );