R help - Jan 2011 - Learn Vectorization (Vectorize)

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)
    }
   
  }
}
sr<-matrix(data=seq(from=1,to=9),nrow=3,ncol=3,byrow=TRUE)
remap(sr)

Regards
Alex

Try this:

expand.grid(seq(startpos, endpos, by = diff(c(startpos, endpos)) /
nrow(sr)),
          seq(startpos, endpos, by = diff(c(startpos, endpos)) / nrow(sr)))

On Tue, Jan 25, 2011 at 1:29 PM, Alaios <alaios@yahoo.com> wrote:
> 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)
>    }
>
>  }
> }
> sr<-matrix(data=seq(from=1,to=9),nrow=3,ncol=3,byrow=TRUE)
> remap(sr)
>
> Regards
> Alex
>
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>


-- 
Henrique Dallazuanna
Curitiba-Paraná-Brasil
25° 25' 40" S 49° 16' 22" O

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