[R] Alternative to apply in base R

[Doran, Harold]

Well, I wish R-help had a “like” button as I would most certainly like
this reply :)

As usual, you’re right. I should have added a disclaimer that “in this
instance” there are 7 columns as the function I wrote evaluates an
N-dimensional integral and so as the dimensions change, so do the number
of columns in this matrix (plus another factor). But the number of columns
is never all that large.



On 11/8/16, 4:37 PM, "peter dalgaard" <pdalgd at gmail.com> wrote:

>
>> 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]]
>>> 
>>> ______________________________________________
>>> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
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>>> PLEASE do read the posting guide
>>> http://www.R-project.org/posting-guide.html
>>> and provide commented, minimal, self-contained, reproducible code.
>> 
>> ______________________________________________
>> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide
>>http://www.R-project.org/posting-guide.html
>> 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
>
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