[R] Extracting multiple elements from a list

[Liaw, Andy]

Aren't sapply()/lapply() sufficient for this?

> sapply(alist, function(x) x$vec)
     [,1] [,2]
[1,]    1    5
[2,]    2    6
[3,]    3    7
[4,]    4    8
> lapply(alist, function(x) x$vec)
[[1]]
[1] 1 2 3 4

[[2]]
[1] 5 6 7 8

HTH,
Andy

> From: Waichler, Scott R
> 
> 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
> 


------------------------------------------------------------------------------
Notice:  This e-mail message, together with any attachments,...{{dropped}}