On Dec 21, 2011, at 10:34 PM, David A Vavra wrote:
I want to take slices of a multi-dimensional table (or array) without
knowing the number of dimensions in advance.
As a test I tried using (in this example a 3d table):
do.call(`[`, list(tbl, x,NULL,NULL)]
Surely that was meant to be:
do.call(`[`, list(tbl, x,NULL,NULL) )
(This does imply you knew the number of dimensions was 3.)
where I built the list on the fly. It works great as long as I only
want the
first dimension however when I try a different dimension, say with
list(tbl,NULL,x,NULL), I get "<0 x 0> matrix" as the result. I
thought this
was because I wasn't calling the right function but there is no
`[.table` or
`[.matrix` or even `[.array`.
It is interesting to look at what that returns.
tbl <- array(1:27, c(3,3,3))
x=1
str( do.call(`[`, list(tbl, x,NULL,NULL) ) )
int[1, 0 , 0 ]
It looks as though the Nulls became 0's. So if you wanted to use
do.call(`[` then this succeeds:
> do.call(`[`, list(tbl, x, 1:dim(tbl)[2], 1:dim(tbl)[3]) )
[,1] [,2] [,3]
[1,] 1 10 19
[2,] 4 13 22
[3,] 7 16 25
As does this using the "empty comma" approach:
eval(parse(text= paste("tbl[ " ,x, " , , ]")) )
[,1] [,2] [,3]
[1,] 1 10 19
[2,] 4 13 22
[3,] 7 16 25
(Which after looking at the `r.utils::extract` code suggested by
Bengtsson, was what he did .... after considerably better sanity
checking than above.)
Am I going about this the wrong way?
DAV
[[alternative HTML version deleted]]
--
David Winsemius, MD
West Hartford, CT
______________________________________________
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
