docs: public static List<Writable> sampleInvalidFromColumnSequence(int numToSample, String columnName, Schema schema,
                      JavaRDD<List<List<Writable>>> data) {
          JavaRDD<List<Writable>> flattened = data.flatMap(new SequenceFlatMapFunction());
          return sampleInvalidFromColumn(numToSample, columnName, schema, flattened);
      }