[R] R performance--referred from Bioconductor listserv

[Robert Gentleman]

Hi,
 Speed is an issue and large data sets are problematic. But I don't
 think that they are the entire problem here. Much more of the problem
 is that we don't yet know how to efficiently normalize microarrays
 and to estimate gene expression data. We're still trying to get it
 right rather than get it fast. There is not a lot of point in
 optimizing an algorithm that has a short shelf-life. And I don't
 think that anyone yet knows just which one will win.

 So, some of the issues are whether algorithms can be improved (and
they probably can; some form of binning would undoubtedly help with a
lot of what is going on in microarray analyses, but that requires that
the technology be somewhat more mature than it is now, at least that
is my view). 

Some gains can be made by cleaning up inefficient code (and newer
versions of the affy package have had some of that done). You can
explore this yourself (and I expect it is a bit more interesting than
benchmarking). The commands below profile the example and the output
(cut short) shows where time is being spent (interested readers are
referred to the man page). 

library(affy)
Rprof()
example(expresso)
Rprof(NULL)
summaryRprof()



$by.self
                                 self.time self.pct total.time
				 total.pct
"fft"                                 1.45     16.8       1.55
17.9
"read.dcf"                            0.42      4.9       0.63
7.3
".C"                                  0.35      4.1       0.35
4.1
"*"                                   0.30      3.5       0.30
3.5
"ifelse"                              0.28      3.3       0.87
10.1
"unique.default"                      0.28      3.3       0.30
3.5
":"                                   0.26      3.0       0.26
3.0
"names<-"                             0.23      2.7       0.28
3.3
"rep.default"                         0.23      2.7       0.23
2.7
"structure"                           0.23      2.7       1.08
12.5


So the bulk of the time is spent if fft; I think the first f is
important so you are unlikely to gain much there, the rest of the
self.time numbers suggest that there are not many gains to be had,
maybe a 20% gain with some serious reworking, maybe more.

But in other cases profiling is a great help (we recently made pretty
minor changes that resulted in major improvements),

 Robert

On Wed, Dec 03, 2003 at 07:31:49PM -0500, Michael Benjamin wrote:
> Hi, all--
>  
> I wanted to start a (new) thread on R speed/benchmarking.  There is a
> nice R benchmarking overview at
> http://www.sciviews.org/other/benchmark.htm, along with a free script so
> you can see how your machine stacks up.
>  
> Looks like R is substantially faster than S-plus.
>  
> My problem is this: with 512Mb and an overclocked AMD Athlon XP 1800+,
> running at 588 SPEC-FP 2000, it still takes me 30 minutes to analyze 4Mb
> .cel files x 120 files using affy (expresso).  Running svm takes a
> mighty long time with more than 500 genes, 150 samples.
>  
> Questions:
> 1) Would adding RAM or processing speed improve performance the most?
> 2) Is it possible to run R on a cluster without rewriting my high-level
> code?  In other words,
> 3) What are we going to do when we start collecting terabytes of array
> data to analyze?  There will come a "breaking point" at which desktop
> systems can't perform these analyses fast enough for large quantities of
> data.  What then?
>  
> Michael Benjamin, MD
> Winship Cancer Institute
> Emory University,
> Atlanta, GA
>  
>  
> 
> 	[[alternative HTML version deleted]]
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://www.stat.math.ethz.ch/mailman/listinfo/r-help

-- 
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| Robert Gentleman                 phone : (617) 632-5250                   |
| Associate Professor              fax:   (617)  632-2444                   |
| Department of Biostatistics      office: M1B20                            |
| Harvard School of Public Health  email: rgentlem at jimmy.harvard.edu        |
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