On Tue, 8 Nov 2016, Doran, Harold 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)
If the real example has only 10 columns, try this:
y <- mm[,1]
for (i in 2:10) y[] <- y*mm[,i]
all.equal(y,rn)
If it has many more columns, I would `reach out' to the inline package and
write 3 lines of C or Fortran to do the operation.
HTH,
Chuck
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