[R] Slow computation in for loop
Yves Brostaux
brostaux.y at fsagx.ac.be
Wed May 28 10:29:34 CEST 2003
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 ?
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