[R] extracting vectors from lists of lists

[David Winsemius]

On Dec 11, 2009, at 5:33 PM, Jennifer Young wrote:

> Good evening
>
> I often have as output from simulations a list of various values,  
> vectors
> and matrices.
> Supposing that I then run said simulation several times, I often  
> want to
> extract a particular result from each simulation for plotting and,
> ideally, put it in a matrix.
>
> A simple example
>
> v1 <- 1:5
> v2 <- 6:10
> other1 <- "stuff"
> other2 <- "stuff"
>
> set1 <- list(v1,other1)
> names(set1) <- c("vec","other")
> set2 <- list(v2,other2)
> names(set2) <- c("vec","other")
>
> output <- list(set1, set2)
>
>
> Is there some form of lapply() that will allow me to extract v1 and v2
> (ie, the $vec elements) from both sets?
> Bonus if I can then put it into a matrix tidily.

 > matrix(unlist(lapply(output, "[", "vec")), ncol=2)
      [,1] [,2]
[1,]    1    6
[2,]    2    7
[3,]    3    8
[4,]    4    9
[5,]    5   10

Or maybe even more directly:

 > sapply(output, "[[", "vec")
      [,1] [,2]
[1,]    1    6
[2,]    2    7
[3,]    3    8
[4,]    4    9
[5,]    5   10

-- 
David Winsemius, MD
Heritage Laboratories
West Hartford, CT