void populateSimpleDataFrame(DataFrame& df)
 {
   // create a very simple data frame were the first factor is perfect and the others are 
   // garbage
   df.addDataVector("a", DblVec(0, 1, 3));
   df.addDataVector("a", DblVec(0, 2, 2));
   df.addDataVector("a", DblVec(0, 3, 1));
   df.addDataVector("b", DblVec(1, 1, 3));
   df.addDataVector("b", DblVec(1, 2, 2));
   df.addDataVector("b", DblVec(1, 3, 1));
   std::vector<std::string> factorLabels;
   factorLabels.push_back("f1");
   factorLabels.push_back("f2");
   factorLabels.push_back("f3");
   df.setFactorLabels(factorLabels);
 }