Re: [R] Extracting multiple elements from a list

[Roger D. Peng]

For the first case, I actually do this pretty often and usually use 
something like:

as.vector(sapply(alist, "[[", "vec"))

For the second case, I think you just need to use lapply():

alist <- lapply(seq(along = alist), function(i)
                alist[[i]]$name <- new.names[i])
-roger

Waichler, Scott R wrote:
For a long time I've wanted a way to conveniently extract multiple elements
from a list, which [[ doesn't allow.  Can anyone suggest an efficient
function to do this?  Wouldn't it be a sensible addition to R?
For example,

alist <- list()
alist[[1]] <- list()
alist[[1]]$name <- "first"
alist[[1]]$vec <- 1:4
alist[[2]] <- list()
alist[[2]]$name <- "second"
alist[[2]]$vec <- 5:8
both.vec <- c(alist[[1]]$vec, alist[[2]]$vec)
Can I get both.vec without c() or an explicit loop?

and

new.names <- c("one", "two")
alist[[1]]$name <- new.names[1]
alist[[2]]$name <- new.names[2]
Could I assign the new values in a quasi-vectorized way?

Thanks,
Scott Waichler
Pacific Northwest National Laboratory
Richland, WA   USA
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