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

If you are using for loops, you are most likely coding R as if it was C or Java or something else. R code that is properly vectorised is extremely fast.

Take for example these two simple bits of code to generate a list of 10,000 integers in sequence:

The first code example is how one would code a loop using a traditional coding paradigm. It takes 28 seconds to complete

system.time({
    a <- NULL
    for(i in 1:1e5)a[i] <- i
})
   user  system elapsed 
  28.36    0.07   28.61 

You can get an almost 100-times improvement by the simple action of pre-allocating memory:

system.time({
    a <- rep(1, 1e5)
    for(i in 1:1e5)a[i] <- i
})

   user  system elapsed 
   0.30    0.00    0.29 

But using the base R vector operation using the colon operator : this operation is virtually instantaneous:

system.time(a <- 1:1e5)

   user  system elapsed 
      0       0       0