Bonjour Christophe,
NA and NaN are different things... Actually this is tricky because NA is
implemented as a special kind of NaN :
See this extract of R_ext/Arith.h :
int R_IsNA(double); /* True for R's NA only */
int R_IsNaN(double); /* True for special NaN, *not* for NA */
int R_finite(double); /* True if none of NA, NaN, +/-Inf */
#define ISNA(x) R_IsNA(x)
/* ISNAN(): True for *both* NA and NaN.
NOTE: some systems do not return 1 for TRUE.
Also note that C++ math headers specifically undefine
isnan if it is a macro (it is on OS X and in C99),
hence the workaround. This code also appears in Rmath.h
*/
#ifdef __cplusplus
int R_isnancpp(double); /* in arithmetic.c */
# define ISNAN(x) R_isnancpp(x)
#else
# define ISNAN(x) (isnan(x)!=0)
#endif
Romain
PS: the question would be more appropriate in R-devel.
On 01/22/2010 11:14 AM, Christophe Genolini wrote:
Hi the list,
I need to write some efficient distances function, so I read the code
for the Euclidean distance.
I do not understand the purpose of the line 11 : if x[i] and y[i] are
not NA (line 9), can dev be NA ?
Christophe
#define both_FINITE(a,b) (R_FINITE(a) && R_FINITE(b))
#define both_non_NA(a,b) (!ISNAN(a) && !ISNAN(b))
1. static double R_euclidean2(double *x, double *y, int taille)
2. {
3. double dev, dist;
4. int count, i;
5.
6. count= 0;
7. dist = 0;
8. for(i = 0 ; i < taille ; i++) {
9. if(both_non_NA(x[i], y[i])) {
10. dev = (x[i] - y[i]);
11. if(!ISNAN(dev)) {
12. dist += dev * dev;
13. count++;
14. }
15. }
16. }
17. if(count == 0)return NA_REAL;
18. if(count != taille) dist /= ((double)count/taille);
19. return sqrt(dist);
20.}
--
Romain Francois
Professional R Enthusiast
+33(0) 6 28 91 30 30
http://romainfrancois.blog.free.fr
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