This is my first time to ask for help in the R mailing list, so sorry for my
misbehavior.
The question is actually an example of the apply function embedded in R. Code
is here:
> x <- cbind(x1 = 3, x2 = c(4:1, 2:5)) > dimnames(x)[[1]] <- letters[1:8] > x
> x1 x2 a 3 4 b 3 3 c 3 2 d 3 1 e 3 2 f 3 3 g 3 4 h 3 5 > cave
> <- function(x, c1, c2) c(mean(x[c1]), mean(x[c2])) > apply(x,1, cave,
> c1="x1", c2=c("x1","x2")) a b c d e f g h [1,] 3.0 3 3.0 3 3.0 3
> 3.0 3 [2,] 3.5 3 2.5 2 2.5 3 3.5 4 > x["x1"] [1] NA > mean(x["x1"]) [1] NA >
> mean(x[c("x1", "x2")]) [1] NA
What confused me is how do apply work to deal with x[c1] and x[c2] (the output
seems unchanged) ? Why can't I call them out the apply function ?
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