The function recolor colors id.target in accordance with the
most likely candidate in id.class.
Note that if scatter is present, then the class given by 0 is represented
as scatter and it is assumed to be the same for both classifications.
The function rematch returns a list as id.trcl and
id.prcl. It is the heart of the recolor function
and is usually called from recolor.
The function recode reoders classes to eliminate group ids without
any members. It is assumed that the group ids are integers.