diegoripley/tippecanoe
1
0
Fork 0
mirror of https://github.com/felt/tippecanoe.git synced 2026-10-06 10:25:41 +02:00
Code Issues Packages Projects Releases Wiki Activity

Multithreaded standard deviation is consistent now

Browse Source
This commit is contained in:
Erica Fischer
2023-02-09 12:14:54 -08:00
parent 07ef9f4a3c
commit b024c515eb
1 changed files with 20 additions and 27 deletions
Download Patch File Download Diff File Expand all files Collapse all files
mbtiles.cpp
+13 -20
View File
@@ -856,38 +856,31 @@ std::map<std::string, layermap_entry> merge_layermaps(std::vector<std::map<std::
fk2->second.count += fk->second.count; fk2->second.count += fk->second.count;
if (fk->second.numeric_count + fk2->second.numeric_count > 0) { if (fk->second.numeric_count + fk2->second.numeric_count > 0) {
// Why is this standard deviation not exactly right?
// Because the subsamples had different means?
// Because the subsamples have different counts?
#if 0
size_t n = fk->second.numeric_count;
size_t m = fk2->second.numeric_count;
double s2x = fk->second.m2;
double s2y = fk2->second.m2;
double xmean = fk->second.mean;
double ymean = fk2->second.mean;
fk2->second.m2 = ((n - 1) * s2x + (m - 1) * s2y) / (n + m - 1) +
((n * m) * pow(xmean - ymean, 2) /
((n + m) * (n + m - 1)));
#endif
// https://math.stackexchange.com/questions/2971315/how-do-i-combine-standard-deviations-of-two-groups // https://math.stackexchange.com/questions/2971315/how-do-i-combine-standard-deviations-of-two-groups
size_t n1 = fk->second.numeric_count; size_t n1 = fk->second.numeric_count;
size_t n2 = fk2->second.numeric_count; size_t n2 = fk2->second.numeric_count;
if (n1 == 0) {
// fk2 is already correct
} else if (n2 == 0) {
// move fk to fk2
fk2->second.m2 = fk->second.m2;
} else {
double var_x1 = fk->second.m2 / n1; double var_x1 = fk->second.m2 / n1;
double var_x2 = fk2->second.m2 / n2; double var_x2 = fk2->second.m2 / n2;
double mean_x1 = fk->second.mean; double mean_x1 = fk->second.mean;
double mean_x2 = fk2->second.mean; double mean_x2 = fk2->second.mean;
double mean_x = (n1 * mean_x1 + n2 * mean_x2) / (n1 + n2); double mean_x = (n1 * mean_x1 + n2 * mean_x2) / (n1 + n2);
double q1 = (n1 - 1) * var_x1 + n1 * mean_x1 * mean_x1; // stack overflow uses n1 - 1 and n2 - 1
double q2 = (n2 - 1) * var_x2 + n2 * mean_x2 * mean_x2; double q1 = (n1) * var_x1 + n1 * mean_x1 * mean_x1;
double q2 = (n2) * var_x2 + n2 * mean_x2 * mean_x2;
double qc = q1 + q2; double qc = q1 + q2;
double sc = sqrt((qc - (n1 + n2) * mean_x * mean_x) / (n1 + n2 - 1)); // stack overflow uses n1 + n2 - 1
double sc = sqrt((qc - (n1 + n2) * mean_x * mean_x) / (n1 + n2));
fk2->second.m2 = sc * sc * (n1 + n2); fk2->second.m2 = sc * sc * (n1 + n2);
}
fk2->second.mean = ( fk2->second.mean = (
fk2->second.mean * fk2->second.numeric_count + fk2->second.mean * fk2->second.numeric_count +