[R] Slow computation in for loop

[Yves Brostaux]

Dear members,

I'm using R to do some test computation on a set of parameters of a 
function. This function is included in three for() loops, first one for 
replications, and the remaining two cycling through possible parameters 
values, like this :

for (k in replicates) {
   data <- sampling from a population
   for (i in param1) {
     for (j in param2) {
        result <- function(i, j, data)
     }
   }
}

With the 'hardest' set of parameters, a single computation of the function 
take about 16s on an old Sun Sparc workstation with 64 Mb RAM and don't 
access a single time to disk.

But when I launch the for() loops (which generate 220 function calls), disk 
gets very sollicitated and the whole process takes as much as 8 to 10 
hours, instead of the expected 1 hour.

What's wrong here ? Is there a thing I don't know about for() loops, and a 
way to correct it ?