Double for-loop operation in R (with an example)

Question

Please look at the following small working example:

#### Pseudo data
nobs1 <- 4000
nobs2 <- 5000
mylon1 <- runif(nobs1, min=0, max=1)-76
mylat1 <         


        

Answer 1

I ran this 3 times, once as you have here, once loading up library compiler (in base R) and running enableJIT(3), and running (with enableJIT) after compiling your thedistance function with cmpfun() (in compiler). The results are (respectively):

> proc.time() - ptm
   user  system elapsed 
 335.26    0.17  339.83

> proc.time() - ptm
   user  system elapsed 
 120.73    0.12  122.52 

> proc.time() - ptm
   user  system elapsed 
 117.86    0.12  118.95 

The difference with 2 and 3 is neglible, as I think enableJIT just compiles the function anyway, but it looks like there is a decent improvement with enableJIT alone. so just throw

library(compiler)

enableJIT(3)

at the top of your code.

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