[R] Code of sample() in C
Paul Smith
phhs80 at gmail.com
Mon Apr 6 15:11:39 CEST 2009
Thanks again, Ranjan. I am wondering whether the seed can be set
(renewed) with GetRNGstate(). Furthermore, I would like to understand
why I am getting the reported compilation errors when I insert
GetRNGstate() in my code.
Paul
On Mon, Apr 6, 2009 at 12:17 PM, Ranjan Maitra <maitra at iastate.edu> wrote:
> Hi Paul,
>
> I believe that you may need to set seed differently when you call the R
> math library as standalone. Specifically, you need to do the following
> (or rather, the following works):
>
> unsigned int seed1, seed2;
> FILE *fran;
>
> fran = fopen("random.seed","r");
> fscanf(fran, "%u %u", &seed1, &seed2);
> fclose(fran);
>
> set_seed(seed1, seed2);
>
> where random.seed is the file containing two large integers.
>
> and after I am done, I usually add the following towards the end of the
> main program....
>
> get_seed(&seed1, &seed2);
>
> fran=fopen("random.seed", "w");
> fprintf(fran, "%d %d\n", seed1, seed2);
> fclose(fran);
>
> You will again need to include Rmath.h and declare the standalone parameter in the calling program also.
>
>
> HTH!
>
> Best wishes,
> Ranjan
>
>
> On Mon, 6 Apr 2009 10:41:19 +0100 Paul Smith <phhs80 at gmail.com> wrote:
>
>> Thanks, Ranjan! I have tried to use the function SampleNoReplace in
>> random.c, which seems to work, except that I get always the same
>> random numbers (with your code the same happens). (My code is below.).
>>
>> I have read the documentation ("Writing R extensions"), where it is advised:
>>
>> «The interface to R’s internal random number generation routines is
>>
>> double unif_rand();
>> double norm_rand();
>> double exp_rand();
>>
>> giving one uniform, normal or exponential pseudo-random variate.
>> However, before these are used, the user must call
>>
>> GetRNGstate();
>>
>> and after all the required variates have been generated, call
>>
>> PutRNGstate();»
>>
>> However, when I use GetRNGstate() and PutRNGstate(), I get the following errors:
>>
>> $ gcc -I/usr/include/R -o myprog myprog.c -lRmath -lm
>> /tmp/cc6CMnlh.o: In function `main':
>> myprog.c:(.text+0x30): undefined reference to `GetRNGstate'
>> myprog.c:(.text+0x57): undefined reference to `PutRNGstate'
>> collect2: ld returned 1 exit status
>> $
>>
>> Any ideas?
>>
>> Paul
>>
>> --------------------------------------
>>
>> #include <stdio.h>
>> #include <stdlib.h>
>> #include <R.h>
>> #include <Rmath.h>
>> #define MATHLIB STANDALONE
>> #include <math.h>
>>
>> void snr(int k, int n, int *y, int *x);
>>
>> int main()
>> {
>>
>> int *x = malloc(50*sizeof(int));
>> int *y = malloc(5*sizeof(int));
>> int i;
>>
>> GetRNGstate();
>> snr(5,50,y,x);
>> PutRNGstate();
>>
>> for(i=0;i<5;++i)
>> printf("%d ",y[i]);
>>
>> free(x);
>> free(y);
>>
>> return 0;
>>
>> }
>>
>>
>> void snr(int k, int n, int *y, int *x)
>> {
>> int i, j;
>> for (i = 0; i < n; i++)
>> x[i] = i;
>> for (i = 0; i < k; i++) {
>> j = n * unif_rand();
>> y[i] = x[j] + 1;
>> x[j] = x[--n];
>> }
>> }
>>
>> --------------------------------------
>>
>>
>>
>> On Sun, Apr 5, 2009 at 11:00 PM, Ranjan Maitra <maitra at iastate.edu> wrote:
>> > I presume you mean sampling without replacement? The following
>> > (adapted from the file you asked for) will do it, but you will need to
>> > incorporate Rmath as standalone in order to get runif to work.
>> >
>> > This function will give you k indices from n, sampled WOR. Thus, n = 50
>> > for you and k = 5. You will get a vector y of length 5 (a pointer of int
>> > actually) which will contain these indices.
>> >
>> > Thus you will define a vector z (of length 50) which is 1:50, and then
>> > using the function, your SRWOR sample will be z[y[i]] where i = 0,
>> > 1,...4.
>> >
>> > I haven't tried this function out much myself, so YMMV.
>> >
>> > HTH!
>> >
>> > Best wishes,
>> > Ranjan
>> >
>> >
>> >
>> > #include <stdlib.h>
>> > #ifndef USING_RLIB
>> > #define MATHLIB_STANDALONE 1 /*It is essential to have this before the call
>> > to the Rmath's header file because this decides
>> > the definitions to be set. */
>> > #endif
>> > #include <Rmath.h>
>> >
>> > /* Note that use of this function involves a prior call to the Rmath library to
>> > get the seeds in place. It is assumed that this is done in the calling
>> > function. */
>> >
>> > /* Equal probability sampling; without-replacement case */
>> > /* Adapted from the R function called SampleNoReplace */
>> >
>> > /**
>> > * Stores k out of n indices sampled at random without replacement
>> > * in y.
>> > */
>> > int srswor(int n, int k, int *y)
>> > {
>> > if (k > n) {
>> > return 1;
>> > }
>> > else {
>> > const double len = (double) n;
>> > int i;
>> > int* x = malloc(n * sizeof(int));
>> > if (!x) {
>> > return 2;
>> > }
>> >
>> > for (i = 0; i < n; ++i) x[i] = i;
>> >
>> > for (i = 0; i < k; ++i) {
>> > const int j = (int)(len * runif(0.0, 1.0));
>> > y[i] = x[j];
>> > x[j] = x[--n];
>> > }
>> > free(x);
>> > }
>> > return 0;
>> > }
>> >
>> >
>> >
>> > On Sun, 5 Apr 2009 20:11:04 +0100 Paul Smith <phhs80 at gmail.com> wrote:
>> >
>> >> Thanks, Ranjan. Got it!
>> >>
>> >> I am now wondering whether there is some simpler way of implementing
>> >> the following in C:
>> >>
>> >> sample(1:50,5)
>> >>
>> >> Paul
>> >>
>> >>
>> >> On Sun, Apr 5, 2009 at 4:10 PM, Ranjan Maitra <maitra at iastate.edu> wrote:
>> >> > Hi Paul,
>> >> >
>> >> > It is in the main/src/random.c file of the source code.
>> >> >
>> >> > HTH!
>> >> > Best wishes,
>> >> > Ranjan
>> >> >
>> >> > On Sun, 5 Apr 2009 15:35:25 +0100 Paul Smith <phhs80 at gmail.com> wrote:
>> >> >
>> >> >> Dear All,
>> >> >>
>> >> >> I would like to use the function sample() in a program written in C.
>> >> >> Is there somewhere the code of sample() written in C?
>> >> >>
>> >> >> Thanks in advance,
>> >> >>
>> >> >> Paul
>> >> >>
>> >> >> ______________________________________________
>> >> >> R-help at r-project.org mailing list
>> >> >> https://stat.ethz.ch/mailman/listinfo/r-help
>> >> >> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>> >> >> and provide commented, minimal, self-contained, reproducible code.
>> >> >>
>> >> >
>> >> > ______________________________________________
>> >> > R-help at r-project.org mailing list
>> >> > https://stat.ethz.ch/mailman/listinfo/r-help
>> >> > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>> >> > and provide commented, minimal, self-contained, reproducible code.
>> >> >
>> >>
>> >> ______________________________________________
>> >> R-help at r-project.org mailing list
>> >> https://stat.ethz.ch/mailman/listinfo/r-help
>> >> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>> >> and provide commented, minimal, self-contained, reproducible code.
>> >>
>> >
>> > ______________________________________________
>> > R-help at r-project.org mailing list
>> > https://stat.ethz.ch/mailman/listinfo/r-help
>> > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>> > and provide commented, minimal, self-contained, reproducible code.
>> >
>>
>> ______________________________________________
>> R-help at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>>
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
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