docs: public static List<Writable> sampleInvalidFromColumn(int numToSample, String columnName, Schema schema,
                      JavaRDD<List<Writable>> data, boolean ignoreMissing) {
          //First: filter out all valid entries, to leave only invalid entries
          int colIdx = schema.getIndexOfColumn(columnName);
          JavaRDD<Writable> ithColumn = data.map(new SelectColumnFunction(colIdx));
  
          ColumnMetaData meta = schema.getMetaData(columnName);
  
          JavaRDD<Writable> invalid = ithColumn.filter(new FilterWritablesBySchemaFunction(meta, false, ignoreMissing));
  
          return invalid.takeSample(false, numToSample);
      }