how to use list index to get vector

Yes, it works. Althought I can understand the help page of sapply,  I
don't know why it works.  What is "["?

-Luke

On 5/16/05, Gabor Grothendieck <ggrothendieck at gmail.com> wrote:

On 5/16/05, Luke <jyzz88 at gmail.com> wrote:

I have a simple question, but I couldn't find the answer in R manuals.

Assume I have a list:

foo <- list()
foo[[1]] <- c(1, 2, 3)
foo[[2]] <- c(11,22,33)
foo[[3]] <- c(111,222,333)
foo

[[1]]
[1] 1 2 3

[[2]]
[1] 11 22 33

[[3]]
[1] 111 222 333

How to use list index to get a vector of, say, the first elements of
list elements?
That is, how to get a vector c(1, 11, 111) from foo?

foo[[]][1] doesn't work.

Try this:

sapply(foo, "[", 1)