[R] Expanding upon expand.grid()

[Robin Hankin]

Andrew

as.binary <- function(n){if(n==0){return(NULL)
   } else {
   return(c((n%%2),Recall(as.integer(n/2))))}}


might help.


rksh



> 
> Hello All:
> 
> The function expand.grid() does nearly exactly what I want for
> permutation tests I wish to carry out, and it does so quickly when the
> number is kept small as in the example below: 
> 
> expand.grid(rep(list(c(-1, 1)), 3))
> 
>   Var1 Var2 Var3
> 1   -1   -1   -1
> 2    1   -1   -1
> 3   -1    1   -1
> 4    1    1   -1
> 5   -1   -1    1
> 6    1   -1    1
> 7   -1    1    1
> 8    1    1    1
> 
> Understandably, for a larger number--16, for example--the grid expands
> to a 65,536 x 16 = 1,048,576 element array of numbers.
> 
> My question is this: is it possible to compute a grid like the one above
> on a row-by-row basis?  What I would like to do is to iteratively take
> one row at a time, compute its sum, store the computed sum for the row,
> and replace the latest row by the next row. In that way, memory burden
> and computation time would be reduced.
> 
> Thanks for your help,
> ANDREW
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://www.stat.math.ethz.ch/mailman/listinfo/r-help
> 


-- 

Robin Hankin, Lecturer,
School of Geography and Environmental Science
Tamaki Campus
Private Bag 92019 Auckland
New Zealand

r.hankin at auckland.ac.nz
tel 0064-9-373-7599 x6820; FAX 0064-9-373-7042