[R] eager to learn how to use "sapply", "lapply", ...

[Gabor Grothendieck]

Also you don't need the abs since you are
squaring it anyways and seq with length
argument is a bit cleaner:

ix <- seq(Nstart, length = NW)
sum(Y[ix]^ 2)

Also please read the last line on every
message to r-help.  The code in your
post lacks all 4 of the asked for
ingredients:  1. there are no comments,
2. it has lines not subsequently used
(not minimal), 3. it not self-contained
and 4. there is no reproducible
calculation.

On Sun, Apr 26, 2009 at 2:04 PM, jim holtman <jholtman at gmail.com> wrote:
> 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?
>
> ______________________________________________
> 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.
>