By the "null distribution" do you mean that the assignment of each 
observation to a column is equal?  If so, the function sample() might 
serve your needs.  For example:

rows <- 3
cols <- 4
rowtot <- 100

m <- matrix(NA, nrow=rows, ncol=cols)

for(i in seq(rows)) {
        m[i, ] <- tabulate(sample(seq(cols), rowtot, replace=T))
        }

m

     [,1] [,2] [,3] [,4]
[1,]   27   24   25   24
[2,]   19   24   26   31
[3,]   26   26   31   17

Jean


Jim Silverton wrote on 08/29/2011 01:14:28 AM:
> 
> Hi all,
> I have  a 3x4 contingency table with row totals all being 100. I want to
> generate 3 x 4 tables from the null distribution. Which R function can 
do
> this?
> 
> -- 
> Thanks,
> Jim.
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