[R] Alternative to apply in base R

[David Winsemius]

> On Nov 8, 2016, at 7:57 AM, Doran, Harold <HDoran at air.org> wrote:
> 
> 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)

I believe you will find that a for-loop is faster.

library(microbenchmark)
help(pac=microbenchmark)
microbenchmark( forloop={ y = mm[,1]; for (i in 2:dim(mm)[2]) y=mm[,i]}, 
    apply = apply(mm,2,prod) )

+----------
Unit: microseconds
    expr    min      lq     mean  median      uq     max neval cld
 forloop 10.735 11.6450 15.00425 13.1295 13.7455 115.600   100  a 
   apply 60.775 63.2025 71.95027 64.4530 71.3525 209.309   100   b



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David Winsemius
Alameda, CA, USA