Dear Ron, On Wed, Dec 22, 2010 at 1:19 PM, Ron Michael <ron_michae...@yahoo.com> wrote: > Let say, I have a matrix with 8 rows and 6 columns: > >> df1 <- matrix(NA, 8, 4) >> df1 > [,1] [,2] [,3] [,4] > [1,] NA NA NA NA > [2,] NA NA NA NA > [3,] NA NA NA NA > [4,] NA NA NA NA > [5,] NA NA NA NA > [6,] NA NA NA NA > [7,] NA NA NA NA > [8,] NA NA NA NA > > Now I want to get **all possible** ways to fetch 6 cells at a time. Is there > any function to do that? >
A matrix is just a vector, so each possible sample of size 6 from df1 corresponds to a sample of size 6 from the vector 1:32. There are many, many ways to get all of those (there are choose(32,6) such samples). The way I do it is library(prob) urnsamples(1:32, size = 6) and you can find lots of other, faster ways. If you store all of those in a data frame A, say, then you can get all possible samples from df1 with something like apply(A, 2, function(x) df1[x])) The good news is that the result will also be a matrix. Each row will be a possible sample of size 6 from df1. Hope this helps, Jay P.S. Note that urnsamples by default is replace = FALSE, ordered = FALSE, which is how I got away with the short command above. __________________________ G. Jay Kerns, Ph.D. Youngstown State University http://people.ysu.edu/~gkerns/ ______________________________________________ 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.
