bp_activity_get_comments_user_ids()

function bp_activity_get_comments_user_ids() {
	global $activities_template;

	$user_ids = ! empty( $activities_template->activity->children )
		? (array) bp_activity_recurse_comments_user_ids( $activities_template->activity->children )
		: array();

	/**
	 * Filters the list of user IDs for the current activity item.
	 *
	 * @since BuddyPress 1.7.0
	 *
	 * @param array $value Array of unique user IDs for the current activity item.
	 */
	return apply_filters( 'bp_activity_get_comments_user_ids', array_unique( $user_ids ) );
}