public void deleteValue(String subject, String variable)
	{
		int subjectIndex = subjects.indexOf(subject);
		if (subjectIndex == -1)
			return;

		Vector<?> valVector = (values.elementAt(subjectIndex));
		Vector<?> varVector = (variables.elementAt(subjectIndex));

		int valueIndex = varVector.indexOf(variable) ;
		if (valueIndex != -1)
		{
			//delete from variables and values vectors
			valVector.removeElementAt(valueIndex);
			varVector.removeElementAt(valueIndex);
			//delete from lines vector
			int assignmentLine = findAssignmentLine(subject, variable);
			if (assignmentLine != -1)
			{
				lines.removeElementAt(assignmentLine);
			}
			//if the subject is empty, delete it
			if (varVector.size()==0)
			{
				deleteSubject(subject);
			}
			if (saveOnChange) saveFile();
		}
	}