parquet-pig/src/main/java/org/apache/parquet/pig/PigSchemaConverter.java
public MessageType filter(MessageType schemaToFilter, Schema requestedPigSchema) {
    return filter(schemaToFilter, requestedPigSchema, null);
  }
public MessageType filter(MessageType schemaToFilter, Schema requestedPigSchema) {
    return filter(schemaToFilter, requestedPigSchema, null);
  }
filters a Parquet schema based on a pig schema for projection
@param schemaToFilter the schema to be filter
@param requestedPigSchema the pig schema to filter it with
@return the resulting filtered schema