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stats: Add support for quartiles (and thus median)
More stuff, quite useful characteristics of a dataset. Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
This commit is contained in:
Damien Lespiau
parent
3839bacde8
commit
1b8997b3f8
131
lib/igt_stats.c
131
lib/igt_stats.c
@ -23,6 +23,7 @@
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*/
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#include <math.h>
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#include <stdlib.h>
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#include <string.h>
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#include "igt_core.h"
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@ -94,6 +95,7 @@ void igt_stats_init(igt_stats_t *stats, unsigned int capacity)
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void igt_stats_fini(igt_stats_t *stats)
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{
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free(stats->values);
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free(stats->sorted);
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}
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@ -158,6 +160,7 @@ void igt_stats_push(igt_stats_t *stats, uint64_t value)
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stats->values[stats->n_values++] = value;
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stats->mean_variance_valid = false;
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stats->sorted_array_valid = false;
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if (value < stats->min)
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stats->min = value;
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@ -220,6 +223,134 @@ uint64_t igt_stats_get_range(igt_stats_t *stats)
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return igt_stats_get_max(stats) - igt_stats_get_min(stats);
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}
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static int cmp_u64(const void *pa, const void *pb)
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{
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const uint64_t *a = pa, *b = pb;
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if (*a < *b)
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return -1;
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if (*a > *b)
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return 1;
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return 0;
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}
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static void igt_stats_ensure_sorted_values(igt_stats_t *stats)
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{
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if (stats->sorted_array_valid)
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return;
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if (!stats->sorted) {
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stats->sorted = calloc(stats->capacity, sizeof(*stats->values));
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igt_assert(stats->sorted);
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}
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memcpy(stats->sorted, stats->values,
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sizeof(*stats->values) * stats->n_values);
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qsort(stats->sorted, stats->n_values, sizeof(*stats->values), cmp_u64);
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stats->sorted_array_valid = true;
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}
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/*
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* We use Tukey's hinge for our quartiles determination.
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* ends (end, lower_end) are exclusive.
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*/
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static double
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igt_stats_get_median_internal(igt_stats_t *stats,
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unsigned int start, unsigned int end,
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unsigned int *lower_end /* out */,
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unsigned int *upper_start /* out */)
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{
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unsigned int mid, n_values = end - start;
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double median;
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igt_stats_ensure_sorted_values(stats);
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/* odd number of data points */
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if (n_values % 2 == 1) {
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/* median is the value in the middle (actual datum) */
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mid = start + n_values / 2;
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median = stats->sorted[mid];
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/* the two halves contain the median value */
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if (lower_end)
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*lower_end = mid + 1;
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if (upper_start)
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*upper_start = mid;
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/* even number of data points */
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} else {
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/*
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* The middle is in between two indexes, 'mid' points at the
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* lower one. The median is then the average between those two
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* values.
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*/
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mid = start + n_values / 2 - 1;
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median = (stats->sorted[mid] + stats->sorted[mid + 1]) / 2.;
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if (lower_end)
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*lower_end = mid + 1;
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if (upper_start)
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*upper_start = mid + 1;
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}
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return median;
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}
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/**
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* igt_stats_get_quartiles:
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* @stats: An #igt_stats_t instance
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* @q1: (out): lower or 25th quartile
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* @q2: (out): median or 50th quartile
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* @q3: (out): upper or 75th quartile
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*
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* Retrieves the [quartiles](https://en.wikipedia.org/wiki/Quartile) of the
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* @stats dataset.
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*/
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void igt_stats_get_quartiles(igt_stats_t *stats,
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double *q1, double *q2, double *q3)
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{
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unsigned int lower_end, upper_start;
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double ret;
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if (stats->n_values < 3) {
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if (q1)
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*q1 = 0.;
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if (q2)
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*q2 = 0.;
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if (q3)
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*q3 = 0.;
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return;
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}
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ret = igt_stats_get_median_internal(stats, 0, stats->n_values,
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&lower_end, &upper_start);
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if (q2)
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*q2 = ret;
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ret = igt_stats_get_median_internal(stats, 0, lower_end, NULL, NULL);
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if (q1)
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*q1 = ret;
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ret = igt_stats_get_median_internal(stats, upper_start, stats->n_values,
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NULL, NULL);
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if (q3)
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*q3 = ret;
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}
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/**
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* igt_stats_get_median:
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* @stats: An #igt_stats_t instance
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*
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* Retrieves the median of the @stats dataset.
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*/
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double igt_stats_get_median(igt_stats_t *stats)
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{
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return igt_stats_get_median_internal(stats, 0, stats->n_values,
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NULL, NULL);
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}
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/*
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* Algorithm popularised by Knuth in:
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*
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@ -41,8 +41,10 @@ typedef struct {
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unsigned int capacity;
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unsigned int is_population : 1;
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unsigned int mean_variance_valid : 1;
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unsigned int sorted_array_valid : 1;
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uint64_t min, max;
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double mean, variance;
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uint64_t *sorted;
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} igt_stats_t;
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void igt_stats_init(igt_stats_t *stats, unsigned int capacity);
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@ -55,7 +57,10 @@ void igt_stats_push_array(igt_stats_t *stats,
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uint64_t igt_stats_get_min(igt_stats_t *stats);
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uint64_t igt_stats_get_max(igt_stats_t *stats);
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uint64_t igt_stats_get_range(igt_stats_t *stats);
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void igt_stats_get_quartiles(igt_stats_t *stats,
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double *q1, double *q2, double *q3);
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double igt_stats_get_mean(igt_stats_t *stats);
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double igt_stats_get_median(igt_stats_t *stats);
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double igt_stats_get_variance(igt_stats_t *stats);
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double igt_stats_get_std_deviation(igt_stats_t *stats);
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@ -25,6 +25,8 @@
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#include "igt_core.h"
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#include "igt_stats.h"
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#define ARRAY_SIZE(arr) (sizeof(arr)/sizeof(arr[0]))
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static void push_fixture_1(igt_stats_t *stats)
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{
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igt_stats_push(stats, 2);
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@ -78,6 +80,44 @@ static void test_range(void)
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igt_assert(igt_stats_get_range(&stats) == 8);
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}
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/*
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* Examples taken from: https://en.wikipedia.org/wiki/Quartile
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* The values are shifted a bit to test we do indeed start by sorting data
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* set.
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*/
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static void test_quartiles(void)
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{
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static const uint64_t s1[] =
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{ 47, 49, 6, 7, 15, 36, 39, 40, 41, 42, 43 };
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static const uint64_t s2[] = { 40, 41, 7, 15, 36, 39 };
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igt_stats_t stats;
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double q1, q2, q3;
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/* s1, odd number of data points */
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igt_stats_init(&stats, ARRAY_SIZE(s1));
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igt_stats_push_array(&stats, s1, ARRAY_SIZE(s1));
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igt_stats_get_quartiles(&stats, &q1, &q2, &q3);
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igt_assert_eq_double(q1, 25.5);
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igt_assert_eq_double(q2, 40);
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igt_assert_eq_double(q3, 42.5);
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igt_assert_eq_double(igt_stats_get_median(&stats), 40);
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igt_stats_fini(&stats);
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/* s1, even number of data points */
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igt_stats_init(&stats, ARRAY_SIZE(s2));
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igt_stats_push_array(&stats, s2, ARRAY_SIZE(s2));
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igt_stats_get_quartiles(&stats, &q1, &q2, &q3);
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igt_assert_eq_double(q1, 15);
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igt_assert_eq_double(q2, 37.5);
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igt_assert_eq_double(q3, 40);
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igt_assert_eq_double(igt_stats_get_median(&stats), 37.5);
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igt_stats_fini(&stats);
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}
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static void test_mean(void)
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{
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igt_stats_t stats;
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@ -150,6 +190,7 @@ igt_simple_main
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test_init();
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test_min_max();
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test_range();
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test_quartiles();
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test_mean();
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test_invalidate_mean();
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test_std_deviation();
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