code: public static List<Writable> sampleInvalidFromColumn(int numToSample, String columnName, Schema schema,
                      JavaRDD<List<Writable>> data) {
          return sampleInvalidFromColumn(numToSample, columnName, schema, data, false);
      }
docs: Randomly sample a set of invalid values from a specified column.
  Values are considered invalid according to the Schema / ColumnMetaData
  
  @param numToSample    Maximum number of invalid values to sample
  @param columnName     Same of the column from which to sample invalid values
  @param schema         Data schema
  @param data           Data
  @return               List of invalid examples