How to fill matrix with random numbers in R?

Question

expand.grid(i=rexp(5,rate=0.1))

It creates just one col but is there some way to multiply this easily to 5 cols? I mean the matlab-way-of-doing-things

Answer 1

Use the matrix function:

matrix(rexp(200, rate=.1), ncol=20)

ETA: If you want to do it without repeating the 200, you can define a function to do so:

fill.matrix = function(expr, nrow=1, ncol=1) {
    matrix(eval(expr, envir=list(x=nrow*ncol)), nrow=nrow, ncol=ncol)
}

fill.matrix(rexp(x, rate=.1), nrow=10, ncol=20)

The x thus becomes the dummy variable you're talking about. Is that what you're looking for?