R help - Apr 2009 - eager to learn how to use "sapply", "lapply", ...

After a year my R programming style is still very "C like".
I am still writing a lot of "for loops" and finding it difficult to
recognize where, in place of loops, I could just do the
same with one line of code, using "sapply", "lapply", or the
like.
On-line examples for such high level function do not help me.
Even if, sooner or later, I am getting my R scripts to do what I expect, I would
really like to shake my C programming style off.
I am staring at my R script and thinking "how can I improve it ?"
For instance, I have a lot of loops similar to the following one and wonder
whether I can replace them with a proper call to a high level R function that
does the same:

    Nstart <- Nfour/(2^Lev) + 1
     Nfinish <- Nstart -1 + Nfour/(2^Lev)
     LengLev <- Nfinish - Nstart + 1
     NW <- floor(LengLev*N/Nfour)
     if(NW > 0){    
       for(j in Nstart:(Nstart + NW -1)){ 
          Dw <- abs(Y[j])
          Rnorm <- Rnorm + Dw^2
       }
     }


Thank you very much for helping me get better.
Maura





tutti i telefonini TIM!


	[[alternative HTML version deleted]]

I think you can replace your 'for' loop with vectorized operations:

  if(NW > 0){
      Rnorm <- Rnorm + sum(abs(Y[Nstart:(Nstart + NW - 1)])  ^ 2)
    }

On Sun, Apr 26, 2009 at 1:42 PM,  <mauede at alice.it>
wrote:
> After a year my R programming style is still very "C like".
> I am still writing a lot of "for loops" and finding it difficult
to recognize where, in place of loops, I could just do the
> same with one line of code, using "sapply", "lapply",
or the like.
> On-line examples for such high level function do not help me.
> Even if, sooner or later, I am getting my R scripts to do what I expect, I
would really like to shake my C programming style off.
> I am staring at my R script and thinking "how can I improve it ?"
> For instance, I have a lot of loops similar to the following one and wonder
whether I can replace them with a proper call to a high level R function that
does the same:
>
> ? ?Nstart <- Nfour/(2^Lev) + 1
> ? ? Nfinish <- Nstart -1 + Nfour/(2^Lev)
> ? ? LengLev <- Nfinish - Nstart + 1
> ? ? NW <- floor(LengLev*N/Nfour)
> ? ? if(NW > 0){
> ? ? ? for(j in Nstart:(Nstart + NW -1)){
> ? ? ? ? ?Dw <- abs(Y[j])
> ? ? ? ? ?Rnorm <- Rnorm + Dw^2
> ? ? ? }
> ? ? }
>
>
> Thank you very much for helping me get better.
> Maura
>
>
>
>
>
> tutti i telefonini TIM!
>
>
> ? ? ? ?[[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at 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.
>


-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem that you are trying to solve?

Have a look at the plyr package and associated documentation -
http://had.co.nz/plyr

Hadley

On Sun, Apr 26, 2009 at 12:42 PM,  <mauede at alice.it>
wrote:
> After a year my R programming style is still very "C like".
> I am still writing a lot of "for loops" and finding it difficult
to recognize where, in place of loops, I could just do the
> same with one line of code, using "sapply", "lapply",
or the like.
> On-line examples for such high level function do not help me.
> Even if, sooner or later, I am getting my R scripts to do what I expect, I
would really like to shake my C programming style off.
> I am staring at my R script and thinking "how can I improve it ?"
> For instance, I have a lot of loops similar to the following one and wonder
whether I can replace them with a proper call to a high level R function that
does the same:
>
> ? ?Nstart <- Nfour/(2^Lev) + 1
> ? ? Nfinish <- Nstart -1 + Nfour/(2^Lev)
> ? ? LengLev <- Nfinish - Nstart + 1
> ? ? NW <- floor(LengLev*N/Nfour)
> ? ? if(NW > 0){
> ? ? ? for(j in Nstart:(Nstart + NW -1)){
> ? ? ? ? ?Dw <- abs(Y[j])
> ? ? ? ? ?Rnorm <- Rnorm + Dw^2
> ? ? ? }
> ? ? }
>
>
> Thank you very much for helping me get better.
> Maura
>
>
>
>
>
> tutti i telefonini TIM!
>
>
> ? ? ? ?[[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at 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.
>


-- 
http://had.co.nz/