[R] fast subsetting of lists in lists

[Alexander Senger]

Hello,


my data is contained in nested lists (which seems not necessarily to be
the best approach). What I need is a fast way to get subsets from the data.

An example:

test <- list(list(a = 1, b = 2, c = 3), list(a = 4, b = 5, c = 6),
list(a = 7, b = 8, c = 9))

Now I would like to have all values in the named variables "a", that is
the vector c(1, 4, 7). The best I could come up with is:

val <- sapply(1:3, function (i) {test[[i]]$a})

which is unfortunately not very fast. According to R-inferno this is due
to the fact that apply and its derivates do looping in R rather than
rely on C-subroutines as the common [-operator.

Does someone now a trick to do the same as above with the faster
built-in subsetting? Something like:

test[<somesubsettingmagic>]


Thank you for your advice


Alex