Hi,
I am doing some simulations and found a bottle neck in my R script. I made
an example:
> a = matrix(rnorm(5000000),1000000,5)
> tt = Sys.time(); sum(a[,1]*a[,2]*a[,3]*a[,4]*a[,5]); Sys.time() - tt
[1] -1291.026
Time difference of 0.2354031 secs
>
> tt = Sys.time(); sum(apply(a,1,prod)); Sys.time() - tt
[1] -1291.026
Time difference of 20.23150 secs
Is there a faster way of calculating sum of products (of columns, or of
rows)? And is this an expected behavior?
Thanks for your advice in advance,
Young
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