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Hello, I am a new user of R, and I'd be grateful if someone could help me with the following: I would like to compute the mean of variable "trust" in dataframe "foo", but separately for each level of variable V2. That is, I'd like to compute the mean of trust at each level of V2. I have done this: > tmp <- by(foo, foo$V2, function(x) mean(foo$trust, na.rm=T))