In reply to kenny.

Sorry if I was not clear. In data analysis, the data are initially in vectors, not sets. For example, you might have a data set that contains jobs held by males and by females, and you want to compute whether the set of jobs by gender are the same, what is the intersection, what is the set difference, and so forth. Consequently, the functions I mention operate on vectors, not sets. The UNIQUE function returns the mathematical set, so if I want to use "pure" sets, I can convert the vector of data to a set. However, sometimes it is more useful to work directly with the vectors so that you can discover how many "female construction workers" and how many "male nurses" there are in the data set.