R help - Nov 2008 - apply() just loops ?

Dear R users,
I have been diligently using the apply() family in order to avoid explicit
for loops and speed up computation.
However, when I finally inspected the source code for apply, it appears that
the core computation is a simple loop as well.
What am I missing ? Why the often found advice to use apply() instead of
loops and the actually observed empirical  speedups on many tasks ?

Thanks in advance for demystifying,


Markus

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Markus Loecher <mao.loecher <at> gmail.com> writes:
> 
> Dear R users,
> I have been diligently using the apply() family in order to avoid explicit
> for loops and speed up computation.
> However, when I finally inspected the source code for apply, it appears
that
> the core computation is a simple loop as well.
> What am I missing ? Why the often found advice to use apply() instead of
> loops and the actually observed empirical  speedups on many tasks ?
> 
> Thanks in advance for demystifying,
> 
> Markus
> 
Professor Ripley gave the following response to a similar question, that I 
believe will answer your question.

http://finzi.psych.upenn.edu/R/Rhelp02a/archive/76330.html

Mark Lyman

Markus,

You may also want to read the Help Desk article in the 8/1 R-News newsletter. 
It discusses the similarities and differences of *apply and loops and also shows
the slowdowns from some common loops (that *apply tend to avoid).

Hope this helps,

--
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at imail.org
801.408.8111

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of Mark Lyman
> Sent: Wednesday, November 12, 2008 10:44 AM
> To: r-help at stat.math.ethz.ch
> Subject: Re: [R] apply() just loops ?
>
> Markus Loecher <mao.loecher <at> gmail.com> writes:
>
> >
> > Dear R users,
> > I have been diligently using the apply() family in order to avoid
> explicit
> > for loops and speed up computation.
> > However, when I finally inspected the source code for apply, it
> appears that
> > the core computation is a simple loop as well.
> > What am I missing ? Why the often found advice to use apply() instead
> of
> > loops and the actually observed empirical  speedups on many tasks ?
> >
> > Thanks in advance for demystifying,
> >
> > Markus
> >
>
> Professor Ripley gave the following response to a similar question,
> that I
> believe will answer your question.
>
> http://finzi.psych.upenn.edu/R/Rhelp02a/archive/76330.html
>
> Mark Lyman
>
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