Why? (Genuinely curious; your comment is just a throwaway line, but you probably wouldn’t have said it if you didn’t have some real reasons.)

Matlab, R, and S-PLUS are all different animals. They are usually used for different things (and what they are used for can vary from person to person). For instance, I use matlab for object oriented scientific programming, R for quick and dirty (but math intensive) scripts, and S-PLUS for quick and dirty stats intensive scripts. Long story short, S-PLUS is geared towards statistics (better modules, functions, etc). If you do some searching, you'll find that R is actually an offspring of S, with S-PLUS being R's sibling. If one can program in R, picking up S-PLUS should be cake since the syntax and programming hats are similar.

I don't really like to type that much, hence my initial terse commentary--but I can certainly oblige someone who is genuinely interested :-)

> Long story short, S-PLUS is geared towards statistics (better modules, functions, etc).

This is still an extremely uninformative answer. Oh well.

R and S-Plus are very similar. Curious when you would prefer S-plus over R?

S-PLUS objects reside on the hard drive whereas R's are stored entirely in memory. So R is faster for smaller computations but runs against limitations when the data sets are large, though you can use the bigmemory library or store your data in external databases - e.g., SQLite or PostgreSQL and pull off chunks as you need them. R also had a much more extensive library but I heard that S-PLUS (as of version 8) made their program compatible with R so that R's libraries could be used in S-PLUS. Also, R has lexical scoping; I think S-PLUS only has global and local like Matlab. I personally like lexical scoping so can't think of cases when you'd find S-PLUS's scope definition advantageous.