#include "gettext.h"
#define _(msgid) gettext (msgid)
-static const double standard_tick[] = {1, 2, 5, 10};
-
/*
Find a set {LOWER, INTERVAL, N_TICKS} such that:
double *lower, double *interval,
int *n_ticks)
{
- double fitness = DBL_MAX;
- double logrange;
- *n_ticks = 0;
-
assert (high >= low);
+ if ((high - low) < 10 * DBL_MIN)
+ {
+ *n_ticks = 0;
+ *lower = low;
+ *interval = 0.0;
+ return;
+ }
- if ((high - low) < 10 * DBL_MIN) {
- *n_ticks = 0;
- *lower = low;
- *interval = 0.0;
- return;
- }
-
- logrange = floor(log10(high-low));
+ /* Round down the difference between HIGH and LOW to a power of 10, then
+ divide by 10. If HIGH - LOW is a power of 10, then BINTERVAL will be
+ (HIGH - LOW) / 10; otherwise, it will be less than (HIGH - LOW) / 10 but
+ more than (HIGH - LOW) / 100.
+
+ for a range of [5.5,9.2], binterval = 0.1;
+ For a range of [0,10], binterval = 1;
+ for a range of [55,92], binterval = 1;
+ for a range of [0,100], binterval = 10;
+ for a range of [555,922], binterval = 10;
+ and so on. */
+ double binterval = pow (10.0, floor (log10 (high - low)) - 1);
+ double fitness = DBL_MAX;
- /* Find the most pleasing interval */
+ /* Find the most pleasing interval. */
+ static const double standard_tick[] = {1, 2, 5, 10};
for (int i = 0; i < sizeof standard_tick / sizeof *standard_tick; i++)
{
- double cinterval = standard_tick[i] * pow(10.0,logrange-1);
- double clower = floor(low/cinterval) * cinterval;
- int cnticks = ceil((high - clower) / cinterval)-1;
- double cfitness = fabs(7.5 - cnticks);
-
- if (cfitness < fitness) {
- fitness = cfitness;
- *lower = clower;
- *interval = cinterval;
- *n_ticks = cnticks;
- }
+ /* Take a multiple of the basic interval. */
+ double cinterval = standard_tick[i] * binterval;
+
+ /* Make a range by rounding LOW down to the next multiple of CINTERVAL,
+ and HIGH up to the next multiple of CINTERVAL. */
+ double clower = floor (low / cinterval) * cinterval;
+ int cnticks = ceil ((high - clower) / cinterval) - 1;
+
+ /* Compute a score based on considering 7.5 ticks to be ideal. */
+ double cfitness = fabs (7.5 - cnticks);
+
+ /* Choose the lowest score. */
+ if (cfitness < fitness)
+ {
+ fitness = cfitness;
+ *lower = clower;
+ *interval = cinterval;
+ *n_ticks = cnticks;
+ }
}
}
first bin has to be aligned to the ticks.
*/
static int
-hist_find_pretty_no_of_bins(double bin_width_in, double min, double max,
- double *adjusted_min, double *adjusted_max)
+hist_find_pretty_no_of_bins (double bin_width_in, double min, double max,
+ double *adjusted_min, double *adjusted_max)
{
+ /* Choose an initial chart scale, without considering bin width. */
double lower, interval;
int n_ticks;
- double binwidth;
- int nbins;
-
chart_get_scale (max, min, &lower, &interval, &n_ticks);
+ /* Then adjust things. */
+ double binwidth;
if (bin_width_in >= 2 * interval)
{
binwidth = floor(bin_width_in/interval) * interval;
if (*adjusted_min > min)
*adjusted_min = min;
- nbins = ceil((max-*adjusted_min)/binwidth);
+ int nbins = ceil((max-*adjusted_min)/binwidth);
*adjusted_max = nbins*binwidth + *adjusted_min;
/* adjusted_max should never be smaller than max but if it is equal
return nbins;
}
+/* Creates and returns a new histogram for data that ranges from MIN to MAX
+ with a suggested bin width of BIN_WIDTH_IN. The implementation will adjust
+ the bin width. The caller should add each data point to the histogram with
+ histogram_add(), and eventually destroy it with statistic_destroy().
+ Returns NULL if the histogram cannot be created. */
struct histogram *
histogram_create (double bin_width_in, double min, double max)
{
- struct histogram *h;
- struct statistic *stat;
- int bins;
- double adjusted_min, adjusted_max;
-
if (max == min)
{
- msg (MW, _("Not creating histogram because the data contains less than 2 distinct values"));
+ msg (MW, _("Not creating histogram because the data contains less than 2 "
+ "distinct values"));
return NULL;
- }
+ }
assert (bin_width_in > 0);
- bins = hist_find_pretty_no_of_bins(bin_width_in, min, max, &adjusted_min, &adjusted_max);
-
- h = xmalloc (sizeof *h);
+ double adjusted_min, adjusted_max;
+ int bins = hist_find_pretty_no_of_bins (bin_width_in, min, max, &adjusted_min,
+ &adjusted_max);
- h->gsl_hist = gsl_histogram_alloc (bins);
+ struct histogram *h = xmalloc (sizeof *h);
+ *h = (struct histogram) {
+ .parent.destroy = destroy,
+ .gsl_hist = gsl_histogram_alloc (bins),
+ };
/* The bin ranges could be computed with gsl_histogram_set_ranges_uniform,
- but the number of bins is adapted to the ticks of the axis such that for example
- data ranging from 1.0 to 7.0 with 6 bins will have bin limits at
- 2.0,3.0,4.0 and 5.0. Due to numerical accuracy the computed bin limits might
- be 4.99999999 for a value which is expected to be 5.0. But the limits of
- the histogram bins should be that what is expected from the displayed ticks.
- Therefore the bin limits are computed from the rounded values which is similar
- to the procedure at the chart_get_ticks_format. Actual bin limits should be
- exactly what is displayed at the ticks.
- But... I cannot reproduce the problem that I see with gsl_histogram_set_ranges_uniform
- with the code below without rounding...
+ but the number of bins is adapted to the ticks of the axis such that for
+ example data ranging from 1.0 to 7.0 with 6 bins will have bin limits at
+ 2.0,3.0,4.0 and 5.0. Due to numerical accuracy the computed bin limits
+ might be 4.99999999 for a value which is expected to be 5.0. But the limits
+ of the histogram bins should be that what is expected from the displayed
+ ticks. Therefore the bin limits are computed from the rounded values which
+ is similar to the procedure at the chart_get_ticks_format. Actual bin
+ limits should be exactly what is displayed at the ticks. But... I cannot
+ reproduce the problem that I see with gsl_histogram_set_ranges_uniform with
+ the code below without rounding...
*/
- {
- double *ranges = xmalloc (sizeof (double) * (bins + 1));
- double interval = (adjusted_max - adjusted_min) / bins;
- for (int i = 0; i < bins; i++)
- ranges[i] = adjusted_min + interval * i;
- ranges[bins] = adjusted_max;
- gsl_histogram_set_ranges (h->gsl_hist, ranges, bins + 1);
- free (ranges);
- }
-
- stat = &h->parent;
- stat->destroy = destroy;
+ double *ranges = xmalloc (sizeof *ranges * (bins + 1));
+ double interval = (adjusted_max - adjusted_min) / bins;
+ for (int i = 0; i < bins; i++)
+ ranges[i] = adjusted_min + interval * i;
+ ranges[bins] = adjusted_max;
+ gsl_histogram_set_ranges (h->gsl_hist, ranges, bins + 1);
+ free (ranges);
return h;
}
-
projects / pspp / commitdiff