Speed up the loop operation in R

Question

I have a big performance problem in R. I wrote a function that iterates over a data.frame object. It simply adds a new column to a data.frame and a

Answer 1

In R, you can often speed-up loop processing by using the apply family functions (in your case, it would probably be replicate). Have a look at the plyr package that provides progress bars.

Another option is to avoid loops altogether and replace them with vectorized arithmetics. I'm not sure exactly what you are doing, but you can probably apply your function to all rows at once:

temp[1:nrow(temp), 10] <- temp[1:nrow(temp), 9] + temp[0:(nrow(temp)-1), 10]

This will be much much faster, and then you can filter the rows with your condition:

cond.i <- (temp[i, 6] == temp[i-1, 6]) & (temp[i, 3] == temp[i-1, 3])
temp[cond.i, 10] <- temp[cond.i, 9]

Vectorized arithmetics requires more time and thinking about the problem, but then you can sometimes save several orders of magnitude in execution time.