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

 t(apply(t(matrix(rep(c(0,0,1),300),nrow = 3)), 1, function(x) sample(x)))