diff --git a/geojson.cpp b/geojson.cpp
index 956825b..a30a326 100644
--- a/geojson.cpp
+++ b/geojson.cpp
@@ -434,43 +434,12 @@ int serialize_geometry(json_object *geometry, json_object *properties, json_obje
 			}
 
 			if (tas.type >= 0) {
+				type_and_string attrib;
+				attrib.type = metatype[m - 1];
+				attrib.string = metaval[m - 1];
+
 				auto fk = layermap->find(layername);
-
-				auto fka = fk->second.file_keys.find(tas.string);
-				if (fka == fk->second.file_keys.end()) {
-					fk->second.file_keys.insert(std::pair<std::string, type_and_string_stats>(tas.string, type_and_string_stats()));
-					fka = fk->second.file_keys.find(tas.string);
-				}
-
-				if (track) {
-					if (fka == fk->second.file_keys.end()) {
-						fprintf(stderr, "Can't happen (tilestats)\n");
-						exit(EXIT_FAILURE);
-					}
-
-					type_and_string attrib;
-					attrib.type = metatype[m - 1];
-					attrib.string = metaval[m - 1];
-
-					if (attrib.type == mvt_double) {
-						double d = atof(attrib.string.c_str());
-
-						if (d < fka->second.min) {
-							fka->second.min = d;
-						}
-						if (d > fka->second.max) {
-							fka->second.max = d;
-						}
-					}
-
-					if (!fka->second.sample_values.count(attrib)) {
-						if (fka->second.sample_values.size() < 1000) {
-							fka->second.sample_values.insert(attrib);
-						}
-					}
-
-					fka->second.type |= (1 << attrib.type);
-				}
+				add_to_file_keys(fk->second.file_keys, metakey[m - 1], attrib);
 			}
 		}
 	}
diff --git a/mbtiles.cpp b/mbtiles.cpp
index 937156d..17428ed 100644
--- a/mbtiles.cpp
+++ b/mbtiles.cpp
@@ -568,3 +568,35 @@ std::map<std::string, layermap_entry> merge_layermaps(std::vector<std::map<std::
 
 	return out;
 }
+
+void add_to_file_keys(std::map<std::string, type_and_string_stats> &file_keys, std::string const &attrib, type_and_string const &val) {
+	auto fka = file_keys.find(attrib);
+	if (fka == file_keys.end()) {
+		file_keys.insert(std::pair<std::string, type_and_string_stats>(attrib, type_and_string_stats()));
+		fka = file_keys.find(attrib);
+	}
+
+	if (fka == file_keys.end()) {
+		fprintf(stderr, "Can't happen (tilestats)\n");
+		exit(EXIT_FAILURE);
+	}
+
+	if (val.type == mvt_double) {
+		double d = atof(val.string.c_str());
+
+		if (d < fka->second.min) {
+			fka->second.min = d;
+		}
+		if (d > fka->second.max) {
+			fka->second.max = d;
+		}
+	}
+
+	if (!fka->second.sample_values.count(val)) {
+		if (fka->second.sample_values.size() < 1000) {
+			fka->second.sample_values.insert(val);
+		}
+	}
+
+	fka->second.type |= (1 << val.type);
+}
diff --git a/mbtiles.hpp b/mbtiles.hpp
index b482e5e..80dcad7 100644
--- a/mbtiles.hpp
+++ b/mbtiles.hpp
@@ -46,4 +46,6 @@ void aprintf(std::string *buf, const char *format, ...);
 
 std::map<std::string, layermap_entry> merge_layermaps(std::vector<std::map<std::string, layermap_entry> > const &maps);
 
+void add_to_file_keys(std::map<std::string, type_and_string_stats> &file_keys, std::string const &layername, type_and_string const &val);
+
 #endif
diff --git a/tile-join.cpp b/tile-join.cpp
index b6536ff..2a8ce6f 100644
--- a/tile-join.cpp
+++ b/tile-join.cpp
@@ -154,28 +154,11 @@ void handle(std::string message, int z, unsigned x, unsigned y, std::map<std::st
 					types.insert(std::pair<std::string, int>(key, type));
 					key_order.push_back(key);
 
-					auto st = file_keys->second.file_keys.find(key);
-					if (st == file_keys->second.file_keys.end()) {
-						file_keys->second.file_keys.insert(std::pair<std::string, type_and_string_stats>(key, type_and_string_stats()));
-						st = file_keys->second.file_keys.find(key);
-					}
+					type_and_string tas;
+					tas.type = type;
+					tas.string = value;
 
-					if (type == mvt_double) {
-						double d = atof(value.c_str());
-						if (d < st->second.min) {
-							st->second.min = d;
-						}
-						if (d > st->second.max) {
-							st->second.max = d;
-						}
-					}
-
-					if (st->second.sample_values.size() < 1000) {
-						type_and_string tas;
-						tas.type = type;
-						tas.string = value;
-						st->second.sample_values.insert(tas);
-					}
+					add_to_file_keys(file_keys->second.file_keys, key, tas);
 				}
 
 				if (header.size() > 0 && strcmp(key, header[0].c_str()) == 0) {
@@ -223,28 +206,11 @@ void handle(std::string message, int z, unsigned x, unsigned y, std::map<std::st
 								types.insert(std::pair<std::string, int>(sjoinkey, attr_type));
 								key_order.push_back(sjoinkey);
 
-								auto st = file_keys->second.file_keys.find(joinkey);
-								if (st == file_keys->second.file_keys.end()) {
-									file_keys->second.file_keys.insert(std::pair<std::string, type_and_string_stats>(joinkey, type_and_string_stats()));
-									st = file_keys->second.file_keys.find(joinkey);
-								}
+								type_and_string tas;
+								tas.type = outval.type;
+								tas.string = joinval;
 
-								if (st->second.sample_values.size() < 1000) {
-									type_and_string tas;
-									tas.type = outval.type;
-									tas.string = joinval;
-									st->second.sample_values.insert(tas);
-								}
-
-								if (outval.type == mvt_double) {
-									double d = atof(joinval.c_str());
-									if (d < st->second.min) {
-										st->second.min = d;
-									}
-									if (d > st->second.max) {
-										st->second.max = d;
-									}
-								}
+								add_to_file_keys(file_keys->second.file_keys, joinkey, tas);
 							}
 						}
 					}