bp_activity_favorites_upgrade_data()

function bp_activity_favorites_upgrade_data() {
	$bp_activity_favorites = bp_get_option( 'bp_activity_favorites', false );

	if ( ! $bp_activity_favorites ) {
		$args = array(
			'fields' => 'ID'
		);

		// The Query
		$user_query = new WP_User_Query( $args );

		// User Loop
		if ( $user_query->get_results() ) {
			foreach ( $user_query->get_results() as $user_id ) {
				$my_favs = bp_get_user_meta( $user_id, 'bp_favorite_activities', true );

				if ( empty( $my_favs ) || ! is_array( $my_favs ) ) {
					continue;
				}

				foreach ( $my_favs as $fav ) {

					// Update the users who have favorited this activity.
					$users = bp_activity_get_meta( $fav, 'bp_favorite_users', true );
					if ( empty( $users ) || ! is_array( $users ) ) {
						$users = array();
					}
					// Add to activity's favorited users.
					$users[] = $user_id;

					// Update activity meta
					bp_activity_update_meta( $fav, 'bp_favorite_users', array_unique( $users ) );

				}
			}

			bp_update_option( 'bp_activity_favorites', true );
		}
	}
}