R help - Oct 2009 - converting matrix of lists to a regular matrix

Take the following code:
 foo <- list()

foo[[1]] <- list(a=1, b=2)
foo[[2]] <- list(a=11, b=22)
foo[[3]] <- list(a=111, b=222)

result <- do.call(rbind, foo)
result[,'a']

In this case, result[,'a'] shows a list. Is there a more elegant way
such
that result is a "regular" matrix of vectors? I imagine there are
manual
ways of going about this, but I was wondering if there was an obvious step
that I was missing.

Thanks,
Andrew

	[[alternative HTML version deleted]]

Try this:

matrix(list(1, 11, 111, 2, 22, 222), nc = 2, dimnames = list(NULL,
c("a", "b")))

or

out  <- list(1, 11, 111, 2, 22, 222)
dim(out) <- c(3, 2)
colnames(out) <- c("a", "b")

On Sat, Oct 3, 2009 at 7:51 PM, Andrew Yee <yee at post.harvard.edu>
wrote:
> Take the following code:
> ?foo <- list()
>
> foo[[1]] <- list(a=1, b=2)
> foo[[2]] <- list(a=11, b=22)
> foo[[3]] <- list(a=111, b=222)
>
> result <- do.call(rbind, foo)
> result[,'a']
>
> In this case, result[,'a'] shows a list. Is there a more elegant
way such
> that result is a "regular" matrix of vectors? I imagine there are
manual
> ways of going about this, but I was wondering if there was an obvious step
> that I was missing.
>
> Thanks,
> Andrew
>
> ? ? ? ?[[alternative HTML version deleted]]
>
> ______________________________________________
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> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

On Oct 3, 2009, at 7:51 PM, Andrew Yee wrote:
> Take the following code:
> foo <- list()
>
> foo[[1]] <- list(a=1, b=2)
> foo[[2]] <- list(a=11, b=22)
> foo[[3]] <- list(a=111, b=222)
>
Instead, perhaps:

 > do.call(rbind, lapply(foo, unlist))
        a   b
[1,]   1   2
[2,]  11  22
[3,] 111 222

 > do.call(rbind, lapply(foo, unlist))[,"a"]
[1]   1  11 111

> result <- do.call(rbind, foo)
> result[,'a']
class(result) # also matrix
>
> In this case, result[,'a'] shows a list. Is there a more elegant
way
> such
> that result is a "regular" matrix of vectors? I imagine there are
> manual
> ways of going about this, but I was wondering if there was an  
> obvious step
> that I was missing.
Your example shows that a matrix can be constructed around a list,  
although I agree with you that this seems a bit unusual.
-- 

David Winsemius, MD
Heritage Laboratories
West Hartford, CT