Method IsSolutionCompatible in PartialDependencePlotView is slow for datasets with string variables

[gkronber]

Inefficient code leads to blocking GUI.

Steps to reproduce:

1. load a dataset with at least one string variable
2. create two independent regression solutions
3. open the partial dependence plot for one solution and draw the other solution on top of it

The relevant code is:

    private static bool SolutionsCompatible(IEnumerable<IRegressionSolution> solutions) {
      var refSolution = solutions.First();
      var refSolVars = refSolution.ProblemData.Dataset.VariableNames;
      foreach (var solution in solutions.Skip(1)) {
        var variables1 = solution.ProblemData.Dataset.VariableNames;
        if (!variables1.All(refSolVars.Contains))
          return false;

        foreach (var factorVar in variables1.Where(solution.ProblemData.Dataset.VariableHasType<string>)) {
          var distinctVals = refSolution.ProblemData.Dataset.GetStringValues(factorVar).Distinct();
          if (solution.ProblemData.Dataset.GetStringValues(factorVar).Any(val => !distinctVals.Contains(val))) return false;
        }
      }
      return true;
    }

[gkronber]

r17920: cache calculations to improve speed when plotting multiple solutions in a partial dependence plot with factor variables.

[mkommend]

r17938: Corrected typo in RegressionSolutoinPDPView.

[mkommend]

r17939: Simplified source code for checking compatibility of solutions by using Hashset and IsSubset method in PDP controls.

[gkronber]

Reviewed r17938 and r17939

[gkronber]

I tested the implementation and could not reproduce the performance problem anymore.

[gkronber]

r18021: merged r17920,r17938,r17939 from trunk to stable