[R] Learn Vectorization (Vectorize)

Alaios alaios at yahoo.com
Tue Jan 25 16:29:48 CET 2011

Greetings Friends,
I would be grateful if you can help me undestand how to make my R code more efficiently.

I have read in R intoductory tutorial that a for loop is not used so ofter (and is not maybe not that efficient) compared to other languages.

So I am trying to build understanding how to get the equivalent of a for loop using more R-oriented thinking.

If I got it right one way to do that in R is Vectorize. So I have writen a small snippet of code with two nested for loops. I would be grateful if you can help me find the equivalent of this code using Vectorize (or any other R thinking)

My code takes as input a n*m matrix and prints the x,y coordinates where a cells starts and ends.

remap <- function (sr){
# Input this funcion takes as arguments
# sr: map
  startpos<- -1 # 
  endpos<- +1 # 
  stepx<- (endpos - (startpos)) / nrow(sr)
  stepy<- (endpos - (startpos)) / ncol(sr)

  for (i in seq(from=-1,to=1,by=stepx) ) { 
    for (j in seq(from=-1,to=1,by=stepx) ){
       cat(' \n',i,j)


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