David gave a great solution. I think it is better to start from 0 to min(M) instead of from min(M[c(1,3)]) to avoid negative values in the table. If the minimum is in M[1] or M[3], a = 1:min(M). Otherwise, d=1:min(M).
Best, Gang 2014-06-24 13:18 GMT-05:00 David L Carlson <dcarl...@tamu.edu>: > Since a 2x2 table with fixed row and column margins has only one degree of > freedom, it is pretty easy to enumerate them: > > A B > A a c M[3] > B b d M[4] > M[1] M[2] N > > Create a vector of the margins: > M <- c(a+b, c+d, a+c, b+d) > > The number of possible tables is min(M[c(1, 3)])+1 since a cannot be > larger than the first column margin or the first row margin. The +1 > recognizes that a can be 0. > > Given any vector M of marginal values, the 2x2 tables are as follows: > > M <- c(8, 9, 9, 8) # For example > M[1]+M[2]==M[3]+M[4] # Check to make sure these are valid margins > TRUE > all.2x2s <- t(sapply(0:min(M[c(1,3)]), function(i) c(a=i, b=M[1] - i, > c=M[3] - i, d=M[4] - M[1] + i))) > all.2x2s > a b c d > [1,] 0 8 9 0 > [2,] 1 7 8 1 > [3,] 2 6 7 2 > [4,] 3 5 6 3 > [5,] 4 4 5 4 > [6,] 5 3 4 5 > [7,] 6 2 3 6 > [8,] 7 1 2 7 > [9,] 8 0 1 8 > > ------------------------------------- > David L Carlson > Department of Anthropology > Texas A&M University > College Station, TX 77840-4352 > > ----Original Message----- > From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] > On Behalf Of Gabor Grothendieck > Sent: Tuesday, June 24, 2014 12:07 PM > To: Tahira Jamil > Cc: r-help@r-project.org > Subject: Re: [R] Sample all possible contingency tables both margin fixed > > On Tue, Jun 24, 2014 at 10:41 AM, Tahira Jamil <tahja...@gmail.com> wrote: > > Hi, > > > > I am interested in generating all possible contingency table (2 by 2) > with fixed row margins and column margins. Can anyone help me. > > > > If the reason you want this is to sample them then r2dtable can do > that directly. > > ______________________________________________ > 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. > > ______________________________________________ > 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. > [[alternative HTML version deleted]] ______________________________________________ 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.
