docs: public static List<Writable> sampleFromColumn(int count, String columnName, Schema schema,
                      JavaRDD<List<Writable>> data) {
          int colIdx = schema.getIndexOfColumn(columnName);
          JavaRDD<Writable> ithColumn = data.map(new SelectColumnFunction(colIdx));
  
          return ithColumn.takeSample(false, count);
      }