# Re: [R] Generating a new matrix using rbinom and a matrix ofprobabilities.

From: <Bill.Venables_at_csiro.au>
Date: Wed, 12 Mar 2008 06:50:54 +1000

probMatrix <- matrix(runif(5*5), 5, 5) ## sets up the probs binoMatrix <- rbinom(length(probMatrix), 1, probMatrix) ## simulates

dim(binoMatrix) <- dim(probMatrix) ## makes it a matrix also

What doesn't work?

I am having a little trouble getting R to do something without writing a couple of very awkward loops.

I have a matrix of probabilities and I want to generate a new matrix of ones and zeros where each element in the new matrix is the result of a draw from a binomial distribution where the probability of getting a 1 is the corresponding element in the matrix of probabilities.

Example Code:

## First I generate the matrix of probabilities for example purposes.

probMatrix <- matrix(NA,5,5){

for (i in 1:5)

probVectorI <- runif(5,0,1)

probMatrix[i,] <- probVectorI

}

# Now I want to take each element in probMatrix and use it as the
probability parameter in rbinom draw and generate a new matrix. Something like this:

binomialMatrix <- rbinom(1,1,probMatrix)

# But that does not work. I know I can run a loop across each vector
of the matrix, but this seems like an bad way to do this.

```---------------------------End Code--------------------------------

```

So any help would be appreciated.

Thanks,

EG

R-help_at_r-project.org mailing list