public int getCategoryIndex(String nodeName, String category) {
   int index = getVariableSource().getVariableNames().indexOf(nodeName);
   DiscreteVariable variable = (DiscreteVariable) getVariableSource().getVariables().get(index);
   return variable.getCategories().indexOf(category);
 }
  public final DataSet filter(DataSet dataSet) {

    // Why does it have to be discrete? Why can't we simply expand
    // whatever discrete columns are there and leave the continuous
    // ones untouched? jdramsey 7/4/2005
    //        if (!(dataSet.isDiscrete())) {
    //            throw new IllegalArgumentException("Data set must be discrete.");
    //        }

    List<Node> variables = new LinkedList<>();

    // Add all of the variables to the new data set.
    for (int j = 0; j < dataSet.getNumColumns(); j++) {
      Node _var = dataSet.getVariable(j);

      if (!(_var instanceof DiscreteVariable)) {
        variables.add(_var);
        continue;
      }

      DiscreteVariable variable = (DiscreteVariable) _var;

      String oldName = variable.getName();
      List<String> oldCategories = variable.getCategories();
      List<String> newCategories = new LinkedList<>(oldCategories);

      String newCategory = "Missing";
      int _j = 0;

      while (oldCategories.contains(newCategory)) {
        newCategory = "Missing" + (++_j);
      }

      newCategories.add(newCategory);
      String newName = oldName + "+";
      DiscreteVariable newVariable = new DiscreteVariable(newName, newCategories);

      variables.add(newVariable);
    }

    DataSet newDataSet = new ColtDataSet(dataSet.getNumRows(), variables);

    // Copy old values to new data set, replacing missing values with new
    // "MissingValue" categories.
    for (int j = 0; j < dataSet.getNumColumns(); j++) {
      Node _var = dataSet.getVariable(j);

      if (_var instanceof ContinuousVariable) {
        for (int i = 0; i < dataSet.getNumRows(); i++) {
          newDataSet.setDouble(i, j, dataSet.getDouble(i, j));
        }
      } else if (_var instanceof DiscreteVariable) {
        DiscreteVariable variable = (DiscreteVariable) _var;
        int numCategories = variable.getNumCategories();

        for (int i = 0; i < dataSet.getNumRows(); i++) {
          int value = dataSet.getInt(i, j);

          if (value == DiscreteVariable.MISSING_VALUE) {
            newDataSet.setInt(i, j, numCategories);
          } else {
            newDataSet.setInt(i, j, value);
          }
        }
      }
    }

    return newDataSet;
  }