Today I worked on a simulation program which require me to create a matrix by repeating the vector n times (both by row and by col).

Even the task is extremely simple and only take 1 line to finish(10sec), I have to think about should the argument in rep be each or times and should the argument in matrix is nrow or ncol. It distracted me from the original task i am working on.

Just now, I wrote a function rep.row and rep.col to do what I really want to do. Next time, i don’t have to worry about how to use the matrix and rep command to repeat an vector to form a matrix!

Code

rep.row<-function(x,n){
matrix(rep(x,each=n),nrow=n)
}
rep.col<-function(x,n){
matrix(rep(x,each=n), ncol=n, byrow=TRUE)
}

x is the vector to be repeated and n is the number of replication. Example:

> rep.row(1:3,5)
[,1] [,2] [,3]
[1,] 1 2 3
[2,] 1 2 3
[3,] 1 2 3
[4,] 1 2 3
[5,] 1 2 3
> rep.col(1:3,5)
[,1] [,2] [,3] [,4] [,5]
[1,] 1 1 2 2 3
[2,] 1 1 2 3 3
[3,] 1 2 2 3 3

I am sure it should appear in some packages, but it would be faster for me to write it out than find it out!

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