code: public FeatureList selectByGroup(String groupid) {
  		FeatureList list = new FeatureList();
  		for (FeatureI f : this) {
  			if (f.group().equals(groupid)) {
  				list.add(f);
  			}
  		}
  
  		return list;
  	}
docs: Create a list of all features that have the specified group id, as defined by
  the group() method of the features.
  
  @param groupid The group to match.
  @return A list of features having the specified group id.