[R] How can I avoid nested 'for' loops or quicken the process?

Oliver Bandel oliver at first.in-berlin.de
Thu Dec 25 21:20:48 CET 2008

Bert Gunter <gunter.berton <at> gene.com> writes:

> Good advice below! -- after all, the first rule of optimizing code is:
> Don't!
> For the record (yet again), the apply() family of functions (and their
> packaged derivatives, of course) are "merely" vary carefully written for()
> loops: their main advantage is in code readability, not in efficiency gains,
> which may well be small or nonexistent. True efficiency gains require
> "vectorization", which essentially moves the for() loops from interpreted
> code to (underlying) C code (on the underlying data structures): e.g.
> compare rowMeans() [vectorized] with ave() or apply(..,1,mean).

The apply-functions do bring speed-advantages.

This is not only what I read about it,
I have used the apply-functions and really got
results faster.

The reason is simple: an apply-function does
make in C, what otherwise would be done on the level of R
with for-loops.


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