Hi, I've got a dataframe like this: df = data.frame(a=rnorm(100,1),b=rnorm(100,10),c=rnorm(100,100),d=rnorm(100,-100)) and I want to calculate sd1 for (a,b,c) for each entry, and sd2 for (b,c,d) for each entry. I don't seem to find the answer using aggregate or apply, How can I do this? Thanks in advance, Cheers, Albert.