Generate a random matrix in R with m columns and n rows where rows sum to 1

Question

I want to generate an nxm matrix. Suppose its 100x3. I want each row to sum to 1 (so two \"0\"\'s and one \"1\").

sample(c(0,0,1),3) 

will

Answer 1

Since you want single 1 for a row, the problem can be restated to select a column entry randomly that has 1 for each row.

So you can do like,

m <- 3; n<-100    
rand_v <- floor(runif(n)*3)+1
mat <- matrix(0,n,m)
idx <- cbind(1:n,rand_v)
mat[idx] <- 1

Hope this helps.