Combine rownames from different lists in a dataframe - list

Question

I have a question about lists in R. I have a list within 16 list containing a list with variables like this:
x
[[1]]
A 1 3
B 4 2
[[2]]
C 23 4
D 9 22
E 4 54
The A,B,C and D are rownames in the lists. Now I want to create a file that paste only the rownames in a dataframe. Each row in the dataframe contains 1 list in the total list.
A B
C D E
Can anyone help me with this? I thought maybe someting like do.call(rbind, rownames(x))
EDIT! 05-08-2011
Is there a way to save the rownames list by list? So in the end there are no NA's in the data and the data is unequal?
Thank you all!

Answer 1

Making an assumption about the nature of x, if we use:
x <- list(matrix(c(1,4,3,2), ncol = 2,
dimnames = list(c("A","B"), NULL)),
matrix(c(23,9,4,4,22,54), ncol = 2,
dimnames = list(c("C","D","E"), NULL)))
which gives:
> x
[[1]]
[,1] [,2]
A 1 3
B 4 2
[[2]]
[,1] [,2]
C 23 4
D 9 22
E 4 54
Then
> lapply(x, rownames)
[[1]]
[1] "A" "B"
[[2]]
[1] "C" "D" "E"
seems the only plausible answer. Unless we pad the ("A","B") vector with something, we can't use a matrix or a data frame because the component lengths do not match. Hence one of the reasons the do.call() idea fails:
> do.call(rbind, rownames(x))
Error in do.call(rbind, rownames(x)) : second argument must be a list
> do.call(rbind, lapply(x, rownames))
[,1] [,2] [,3]
[1,] "A" "B" "A"
[2,] "C" "D" "E"
Warning message:
In function (..., deparse.level = 1) :
number of columns of result is not a multiple of vector length (arg 1)
To pad the result with NA and get a data frame, we could do:
out <- lapply(x, rownames)
foo <- function(x, max, repl = NA) {
if(length(x) == max)
out <- x
else {
out <- rep(repl, max)
out[seq_along(x)] <- x
}
out
}
out <- lapply(out, foo, max = max(sapply(out, length)))
(out <- do.call(rbind, out))
The last line gives:
> (out <- do.call(rbind, out))
[,1] [,2] [,3]
[1,] "A" "B" NA
[2,] "C" "D" "E"
If you want that nicely printed, then
> print(format(out), quote = FALSE)
[,1] [,2] [,3]
[1,] A B NA
[2,] C D E
is an option inside R.

Answer 2

This should do it:
lapply(x, function(curdfr){paste(rownames(curdfr))})
This results in a vector with each element the space-separated rownames of the elements of the list.

Answer 3

Your sample data:
x <- list(
matrix(c(1,4,3,2), nrow = 2, dimnames = list(LETTERS[1:2])),
matrix(c(23,9,4,4,22,54), nrow = 3, dimnames = list(LETTERS[3:5]))
)
What you want:
unlist(lapply(x, rownames))
Or, if you are keen on do.call, then this is equivalent:
do.call(c, lapply(x, rownames))