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Use circular mean to determine how categorical each attribute is

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This commit is contained in:
Erica Fischer
2022-12-07 11:05:10 -08:00
parent f1df09f147
commit 3ae800745c
2 changed files with 27 additions and 0 deletions
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mbtiles.cpp
+22
View File
@@ -276,6 +276,12 @@ void tilestats(std::map<std::string, layermap_entry> const &layermap1, size_t el
state.json_write_string("attribute");
state.json_write_string(attribute.first);
double xd = attribute.second.xsum / attribute.second.count;
double yd = attribute.second.ysum / attribute.second.count;
double d = sqrt(xd * xd + yd * yd);
printf("%s %0.6f\n", attribute.first.c_str(), d);
size_t val_count = attribute.second.sample_values.size();
if (val_count > max_tilestats_sample_values) {
val_count = max_tilestats_sample_values;
@@ -848,6 +854,22 @@ void add_to_file_keys(std::map<std::string, type_and_string_stats> &file_keys, s
if (fka->second.sample_values.size() > max_tilestats_sample_values) {
fka->second.sample_values.pop_back();
}
unsigned hash = 0;
for (size_t i = 0; i < val.string.size(); i++) {
// https://en.wikipedia.org/wiki/Hash_function#Fibonacci_hashing
hash = hash * 2654435769 + val.string[i];
}
// extra multiply so even single-byte values are distributed
// around the circle rather than clumped together on one side.
hash = hash * 2654435769;
double angle = ((double) hash) / UINT_MAX * 2 * M_PI;
double x = cos(angle);
double y = sin(angle);
fka->second.xsum += x;
fka->second.ysum += y;
fka->second.count++;
}
fka->second.type |= (1 << val.type);
mbtiles.hpp
+5
View File
@@ -22,6 +22,11 @@ struct type_and_string_stats {
double min = INFINITY;
double max = -INFINITY;
int type = 0;
// for circular mean of value hashes
double xsum = 0;
double ysum = 0;
size_t count = 0;
};
struct layermap_entry {