[Rd] R vs. C

[Spencer Graves]

       Another point I have not yet seen mentioned:  If your code is 
painfully slow, that can often be fixed without leaving R by 
experimenting with different ways of doing the same thing -- often after 
using profiling your code to find the slowest part as described in 
chapter 3 of "Writing R Extensions".


       If I'm given code already written in C (or some other language), 
unless it's really simple, I may link to it rather than recode it in R.  
However, the problems with portability, maintainability, transparency to 
others who may not be very facile with C, etc., all suggest that it's 
well worth some effort experimenting with alternate ways of doing the 
same thing in R before jumping to C or something else.


       Hope this helps.
       Spencer


On 1/17/2011 10:57 AM, David Henderson wrote:
> I think we're also forgetting something, namely testing.  If you write your
> routine in C, you have placed additional burden upon yourself to test your C
> code through unit tests, etc.  If you write your code in R, you still need the
> unit tests, but you can rely on the well tested nature of R to allow you to
> reduce the number of tests of your algorithm.  I routinely tell people at Sage
> Bionetworks where I am working now that your new C code needs to experience at
> least one order of magnitude increase in performance to warrant the effort of
> moving from R to C.
>
> But, then again, I am working with scientists who are not primarily, or even
> secondarily, coders...
>
> Dave H
>
>
>
> ----- Original Message ----
> From: Dirk Eddelbuettel<edd at debian.org>
> To: Patrick Leyshock<ngkbr8es at gmail.com>
> Cc: r-devel at r-project.org
> Sent: Mon, January 17, 2011 10:13:36 AM
> Subject: Re: [Rd] R vs. C
>
>
> On 17 January 2011 at 09:13, Patrick Leyshock wrote:
> | A question, please about development of R packages:
> |
> | Are there any guidelines or best practices for deciding when and why to
> | implement an operation in R, vs. implementing it in C?  The "Writing R
> | Extensions" recommends "working in interpreted R code . . . this is normally
> | the best option."  But we do write C-functions and access them in R - the
> | question is, when/why is this justified, and when/why is it NOT justified?
> |
> | While I have identified helpful documents on R coding standards, I have not
> | seen notes/discussions on when/why to implement in R, vs. when to implement
> | in C.
>
> The (still fairly recent) book 'Software for Data Analysis: Programming with
> R' by John Chambers (Springer, 2008) has a lot to say about this.  John also
> gave a talk in November which stressed 'multilanguage' approaches; see e.g.
> http://blog.revolutionanalytics.com/2010/11/john-chambers-on-r-and-multilingualism.html
>
>
> In short, it all depends, and it is unlikely that you will get a coherent
> answer that is valid for all circumstances.  We all love R for how expressive
> and powerful it is, yet there are times when something else is called for.
> Exactly when that time is depends on a great many things and you have not
> mentioned a single metric in your question.  So I'd start with John's book.
>
> Hope this helps, Dirk