Linq to group by two fields and average

Question

I have the following C# models:

public class RawData
{
    public int questionnaireId { get; set; }

    public int coachNodeId { get; set; }

    public int ques         


        

Answer 1

Try following :

            DataTable dt = new DataTable();
            dt.Columns.Add("questionnaireId", typeof(int));
            dt.Columns.Add("coachNodeId", typeof(int));
            dt.Columns.Add("questionnaireNumber", typeof(int));
            dt.Columns .Add("score", typeof(int));

            dt.Rows.Add(new object[] {1,30, 1, 2});
            dt.Rows.Add(new object[] {2,40, 1, 3});
            dt.Rows.Add(new object[] {3,30, 2, 1});
            dt.Rows.Add(new object[] {4,30, 3, 4});
            dt.Rows.Add(new object[] {5,40, 2, 5});
            dt.Rows.Add(new object[] {6,40, 1, 5});
            dt.Rows.Add(new object[] {7,30, 1, 1});
            dt.Rows.Add(new object[] {8,30, 1, 2});
            dt.Rows.Add(new object[] {9,40, 1, 2});
            dt.Rows.Add(new object[] {10,30, 2, 4});

            var averages = dt.AsEnumerable()
                .GroupBy(x => new { coachNodeId = x.Field<int>("coachNodeId"), questionnaireNumber = x.Field<int>("questionnaireNumber") })
                .Select(x => new { coachNodeId = x.Key.coachNodeId, questionnaireNumber = x.Key.questionnaireNumber, average = x.Average(y => y.Field<int>("score")) })
                .ToList();

Answer 2

assuming you have a List<RawData> called list, you are wanting:

var results = list.GroupBy(x => new
                                {
                                     questionnaire = x.questionnaireId,
                                     coach = x.coachNodeId
                                })
                  .Select(x => new AveragedData
                                {
                                     coachNodeId = x.Key.coach,
                                     questionnaireNumber = x.Key.questionnaire,
                                     averageScore = x.Average(xx => xx.score)
                                })
                  .ToList();

Do the grouping, then use a Select to project the data to your type, using LINQ's Average as well.