A quick way to do row repeat and col repeat: 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!

[sourcecod] 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) } [/sourcecod]

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

[sourcecod] > 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 [/sourcecod]