Hi, i got a little question about the NA's in vectors and matrices. When I want to do some operations on a matrix with some NA's it is possible to stripp them before the computation proceed (by na.rm=TRUE). But how can I stripp NA's when I want to proceed a 'if', 'for' or 'while' string? Because when I don't stripp them I always reveive the message :"missing value where TRUE/FALSE needed". I don't know if I can use the method with na.rm=TRUE and if so, how I can do it. Thanks a lot in advance! Matthias Tips