code: private void assign  ( HashMap < String , DBIDs > labelMap , String label , DBIDRef id ) { if ( labelMap . containsKey ( label ) ) { DBIDs exist = labelMap . get ( label ) ; if ( exist instanceof DBID ) { ModifiableDBIDs n = DBIDUtil . newHashSet ( ) ; n . add ( ( DBID ) exist ) ; n . add ( id ) ; labelMap . put ( label , n ) ; } else { assert ( exist instanceof HashSetModifiableDBIDs ) ; assert ( exist . size ( ) > 1 ) ; ( ( ModifiableDBIDs ) exist ) . add ( id ) ; } } else { labelMap . put ( label , DBIDUtil . deref ( id ) ) ; } }