public <T> Map<Object, T> remapKeysByType(String key, Map<Object, T> keyedMap) {
    Map<Object, T> newMap = new LinkedHashMap<>();

    String dataType = keyType.get(key);
    UnaryOperator<Object> parser;

    if (dataType == null || (parser = DataType.from(dataType).parser()) == null) {
      newMap.putAll(keyedMap);
    } else {
      keyedMap.forEach((mapKey, value) -> newMap.put(parser.apply(mapKey), value));
    }

    return newMap;
  }
Returns copy of {@code keyedMap} where the keys have been transformed by the parser associated with {code key}.
planetiler-custommap/src/main/java/com/onthegomap/planetiler/custommap/TagValueProducer.java