woocommerce-hide-shipping-rates-when-free-shipping-is-available-keep-local-pickup.php

/**
 * Hide shipping rates when free shipping is available, but keep "Local pickup" 
 * Updated to support WooCommerce 2.6 Shipping Zones
 * Source: https://woocommerce.com/document/hide-other-shipping-methods-when-free-shipping-is-available/
 */
add_filter( 'woocommerce_package_rates', 'hide_shipping_when_free_is_available', 10, 2 );
function hide_shipping_when_free_is_available( $rates, $package ) {
	$new_rates = array();
	foreach ( $rates as $rate_id => $rate ) {
		// Only modify rates if free_shipping is present.
		if ( 'free_shipping' === $rate->method_id ) {
			$new_rates[ $rate_id ] = $rate;
			break;
		}
	}

	if ( ! empty( $new_rates ) ) {
		//Save local pickup if it's present.
		foreach ( $rates as $rate_id => $rate ) {
			if ('local_pickup' === $rate->method_id ) {
				$new_rates[ $rate_id ] = $rate;
				break;
			}
		}
		return $new_rates;
	}

	return $rates;
}