[R] own function: computing time

[Jan van der Laan]

Did not see a simple way to make it faster. However, this is a piece of 
code which can be made to run much faster in C. See below.

I don't know if you are familiar with running c-code from R. If not, the 
official documentation is in the R Extensions manual. However, this is 
not the most easy documentation for a first read. If you want to use the 
c-code and have problems getting it running, let me/us know your 
operating system and I/we will try to walk you through it.

HTH,
Jan


=== c-code ===
void foo(double* m, int* pn, int* r) {
   int n = *pn;
   double* pm1 = m;
   double* pm2 = m + n;
   int* pr = r;
   for (int i = 0; i < n; ++i, ++pm1, ++pm2, ++pr) {
     *pr = 1;
     double* qm1 = m;
     double* qm2 = m + n;
     for (int j = 0; j < n; ++j, ++qm1, ++qm2) {
       if ((*qm1 > *pm1) && (*qm2 > *pm2)) {
         *pr = 0;
         break;
       }
     }
   }
}

=== r-code ===
dyn.load("rtest.so")

foo <- function(m) {
   n <- dim(m)[1]
   .C("foo",
       as.double(m),
       as.integer(n),
       r = logical(n))$r
}

x <- runif(32000)
y <- runif(32000)
xy <- cbind(x,y)

t1 <- system.time({
     outer <- function(z){
         !any(x > z[1] & y > z[2])
     }
     j <- apply(xy,1, outer)
})

t2 <- system.time({
     j2 <- foo(xy)
})

=== results ===
 > all(j == j2)
[1] TRUE
 > t1
    user  system elapsed
  35.462   0.028  35.549
 > t2
    user  system elapsed
   0.008   0.000   0.008
 >




On 10/10/2012 12:15 PM, tonja.krueger at web.de wrote:
> Hi all,
>
> I wrote a function that actually does what I want it to do, but it tends to be very slow for large amount of data. On my computer it takes 5.37 seconds for 16000 data points and 21.95 seconds for 32000 data points. As my real data consists of 18000000 data points it would take ages to use the function as it is now.
> Could someone help me to speed up the calculation?
>
> Thank you, Tonja
>
> system.time({
> x <- runif(32000)
> y <- runif(32000)
>
> xy <- cbind(x,y)
>
> outer <- function(z){
> !any(x > z[1] & y > z[2])}
> j <- apply(xy,1, outer)
>
> plot(x,y)
> points(x[j],y[j],col="green")
>
> })
>
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