[R] Alternative to apply in base R

[peter dalgaard]

> On 08 Nov 2016, at 21:23 , Doran, Harold <HDoran at air.org> wrote:
> 
> It¹s a good suggestion. Multiplication in this case is over 7 columns in
> the data, but the number of rows is millions. Unfortunately, the values
> are negative as these are actually gauss-quad nodes used to evaluate a
> multidimensional integral.

If there really are only 7 cols, then there's also the blindingly obvious

mm[,1]*mm[,2]*mm[,3]*mm[,4]*mm[,5]*mm[,6]*mm[,7]

-pd


> 
> colSums is better than something like apply(dat, 2, sum); I was hoping
> there was something similar to colSums/rowSums using prod().
> 
> On 11/8/16, 3:00 PM, "Fox, John" <jfox at mcmaster.ca> wrote:
> 
>> Dear Harold,
>> 
>> If the actual data with which you're dealing are non-negative, you could
>> log all the values, and use colSums() on the logs. That might also have
>> the advantage of greater numerical accuracy than multiplying millions of
>> numbers. Depending on the numbers, the products may be too large or small
>> to be represented. Of course, logs won't work with your toy example,
>> where rnorm() will generate values that are both negative and positive.
>> 
>> I hope this helps,
>> John
>> -----------------------------
>> John Fox, Professor
>> McMaster University
>> Hamilton, Ontario
>> Canada L8S 4M4
>> web: socserv.mcmaster.ca/jfox
>> 
>> 
>> ________________________________________
>> From: R-help [r-help-bounces at r-project.org] on behalf of Doran, Harold
>> [HDoran at air.org]
>> Sent: November 8, 2016 10:57 AM
>> To: r-help at r-project.org
>> Subject: [R] Alternative to apply in base R
>> 
>> Without reaching out to another package in R, I wonder what the best way
>> is to speed enhance the following toy example? Over the years I have
>> become very comfortable with the family of apply functions and generally
>> not good at finding an improvement for speed.
>> 
>> This toy example is small, but my real data has many millions of rows and
>> the same operations is repeated many times and so finding a less
>> expensive alternative would be helpful.
>> 
>> mm <- matrix(rnorm(100), ncol = 10)
>> rn <- apply(mm, 1, prod)
>> 
>>       [[alternative HTML version deleted]]
>> 
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> 
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
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> and provide commented, minimal, self-contained, reproducible code.

-- 
Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Office: A 4.23
Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com