search for: surjection

Hello, I am trying to map a factor variable within a data frame to a new variable whose entries are derived from the content of the original variable and there are fewer factors in the new variable. That is, I'm trying to set up a surjection. After first thinking that this would be a common operation and would have a quite simple interface, I can not seem to find one, nor any similar posts on this topic (please correct me if there is something). Therefore, I have written a function to perform this mapping. However, the function I hav...