[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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