# [R-sig-hpc] number of combinations

Amen Alyaari amen.alyaari at bordeaux.inra.fr
Thu Jul 18 13:54:48 CEST 2013

```Hello All,

I have three datasets and would like to know how much N was used in my
calculations.

I read the data into a multi-dimensional array with dimensions (nx, ny,
ntsteps, ndatasets), e.g. with a smaller example dataset:

# nx   ny   nsteps ndatasets
dat = runif(20 * 30 * 100 *  3)
dim(dat) = c(20, 30, 100, 3)
> str(dat)
num [1:20, 1:30, 1:100, 1:3] 0.1834 0.8537 0.0672 0.0734 0.8078 ...
we take advantage of the cor functions and build this function to
compute how many N we have:

cor_withN <- function(...) {
res <- try(cor.test(...)\$parameter+2, silent=TRUE)
ifelse(class(res)=="try-error", NA, res)}
Now we take advantage of the fact that apply also works on
multi-dimensional arrays, not only matrices:
We use apply to iterate over all the x,y,z triples.

result = apply(dat, c(1,2), function(x) cor_withN(x[,1],
x[,2],x[,3]))
> str(cor_result)
logi [1:20, 1:30] NA NA NA NA NA NA ..
so something is wrong by getting NA NA NA NA
if the last line went well! then:      str(cor_result)
should be:

logi [1:20, 1:30] 100 100 100 100 100 ..(nsteps)
Any idea on why I am getting NA or is there another way to do it?

When I tested it with 2 datsets,it went well!

cor_result = apply(dat, c(1,2), function(x) cor_withN(x[,1], x[,2]))
> str(cor_result)
num [1:20, 1:30] 100 100 100 100 100 100 100 100 100 100
so the problem is when I added x[,3]!! Thanks

Thanks alot

```