Class method to return multiple results (lists and multi-dimensional arrays)

Question

I have a class with a method that generates some results and populates both a List and a double[,]. So when doing the calculations, final results are stored into a double[,] but intermediate results in a List.

Something like this:

public double[,] methodOne(Dictionary<string, double> myInputOne, List<double> myInputTwo)
{
List<double> intermediateResults= new List<double>();
double[,] finalResults= new double[rows, cols];

// Do some calculation using myInputOne and myInputTwo

intermediateResults.Add(something);

// Continue the calculation using also intermediateResults
// store results in double[,] finalResults

return results ;
}

This would work only if you want the method to return the results table. But how can I tell the method to return also the List intermediateResults?

I would like this method to return both the intermediate and final results so that they can be used by other methods down the road. Thank you.

Answer 1

Rather than return a single type or a tuple, return a custom object as it will make the calling code more readable:

public class Results
{
    public List<double> IntermediateResults { get; set; }
    public double[,] FinalResults { get; set; }
}

Then your method looks something like:

public Results methodOne(Dictionary<string, double> myInputOne, List<double> myInputTwo)
{
   List<double> intermediateResults = new List<double>();
   double[,] finalResults = new double[rows, cols];

   // Do some calculation using myInputOne and myInputTwo

   intermediateResults.Add(something);

   // Continue the calculation using also intermediateResults
   // store results in double[,] finalResults

   var results = new Results();
   results.FinalResult = finalResult;
   results.IntermediateResults = intermediateResults;

   return results;
}

Answer 2

You could change the return type to Tuple<T1, T2>

So the method declaration would become

public Tuple<List<double>, double[,]> methodOne(Dictionary<string, double> myInputOne, List<double> myInputTwo)

And in turn, you would return

return new Tuple<List<double>, double[,]>(intermediateResults, finalResults);

However, it depends on how you want to use the returned data. If it's not just a short-term result, you're better off just making a custom object, as Ralph Willgoss suggested.

Answer 3

An option to the other provided answers would be the out -keyword. In your case:

public double[,] methodOne(Dictionary<string, double> myInputOne, 
    List<double> myInputTwo, out List<double> intermediateResults)
{
    intermediateResults= new List<double>();
    double[,] finalResults= new double[rows, cols];

    // Do some calculation using myInputOne and myInputTwo

    intermediateResults.Add(something);

    // Continue the calculation using also intermediateResults
    // store results in double[,] finalResults

    return results ;
}

Usage:

List<double> intermediateResults;
double[,] finalResults = methodOne(someDictionary, someList, out intermediateResults);