SV: [R] sample from contingency table

[Regin Reinert]

I have had the same problem and I wrote this function

rmulti <- function(n, size, p)
{
  NrDim <- length(p)
  if(NrDim<2) stop("The simulated variabel has to be at least
2-dimensional")
  res <- matrix(data=NA, nrow=n, ncol=NrDim)
  p <- p/sum(p)
  TempSize <- size
  for(i in 1:NrDim)
  {
    TempP <- p[i]/sum(p[i:NrDim])
    TempBin <- rbinom(n=n, size=TempSize, prob=TempP)
    TempSize <- TempSize-TempBin
    res[,i] <- TempBin
  }
  return(res)
}

# Then you can draw 10 samples like this, whith
# each row representing a contingency table

x <- as.matrix(1:4, nrow=2, ncol=2)
rmulti(10, sum(x), x)


Regin


-----Oprindelig meddelelse-----
Fra: Dirk F. Raetzel [mailto:raetzel at Mathematik.Uni-Marburg.de]
Sendt: 19. september 2000 18:48
Til: R-Help Mailing List
Emne: [R] sample from contingency table


Hello,

I have a multivariate (dim >= 3) discrete distribution
given by a contingency table from which I want to draw independent
random samples. The result should be a data.frame (or array) with each
column representing a dimension.

Before starting to hack some search tree with approbiate
transformations: Is there any built-in function I
have overseen or did anybody program such a function already?

Dirk



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