On Feb 14, 2012, at 8:44 AM, geotheory wrote:
Basic question (if you know the answer)... I am dealing with a list
of
commonly-formatted sub-lists, for example:
l <- list("")
l[[1]] <- c("A1","A2","A3")
l[[2]] <- c("B1","B2","B3")
l[[3]] <- c("C1","B2","B3")
Lets say I need to extract every 2nd item (i.e. A2, B2, C2). [[]]
cannot be
used. l[2] returns practically the same as l[[2]]. Is there a way
to
achieve this without having to loop or convert to data.frame?
Any such extraction would of necessity have a loop-like basis, but
perhaps you meant without an explicit for-loop?
> sapply(l, "[[", 2)
[1] "A2" "B2" "B2"
--
David Winsemius, MD
West Hartford, CT
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