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JonnyTools.h
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25 
26 #ifndef JONNYTOOLS_H
27 #define JONNYTOOLS_H
28 
29 #include <stdlib.h>
30 
31 /* For use with qsort */
32 int qsort_cmp(const void* x, const void* y)
33 {
34  double xx = *(double*) x, yy = *(double*) y;
35  if (xx < yy) return -1;
36  if (xx > yy) return 1;
37  return 0;
38 }
39 
40 /* Returns the 100*perc-th percentile of array.
41  * array should be sorted, e.g.
42  * qsort(xs, n, sizeof(double), qsort_cmp);
43  * and perc should be a number between 0 and 1.
44  */
45 double getPercentile(const double* array, size_t nel, double perc)
46 {
47  size_t lower_ind = floor(perc * (nel - 1));
48  size_t upper_ind = ceil(perc * (nel - 1));
49  double lambda = (perc * (nel - 1)) - lower_ind;
50  double lower_x = array[lower_ind];
51  double upper_x = array[upper_ind];
52  double percentile = (1 - lambda) * lower_x + lambda * upper_x;
53  // fprintf(stderr, "nel %d perc %f lower_ind %d upper_ind %d lambda %f lower_x %f upper_x %f percentile %f\n",
54  // nel, perc, lower_ind, upper_ind, lambda, lower_x, upper_x, percentile);
55  return percentile;
56 }
57 
58 #endif
int qsort_cmp(const void *x, const void *y)
Definition: JonnyTools.h:32
double getPercentile(const double *array, size_t nel, double perc)
Definition: JonnyTools.h:45