Question

Good morning, I’ve got two lists that I need to merge together and create a data table from, I’ve got the following block of code:

private static DataTable GetDataTable(IList<DataValue> listOneDataValues,
                                            IList<DataValue> listTwoDataValues)
      {
         var dataTable = new DataTable();
         dataTable.Columns.Add("ColumnFromListOne");
         dataTable.Columns.Add("ColumnFromListTwo");
         dataTable.Columns.Add("TimeStamp");

         //Group the lists together
         var query = (from listOne in listOneDataValues
                      from listTwo in listTwoDataValues
                      let columnFromListOne= listOne.DoubleValue
                      let columnFromListTwo= listTwo.DoubleValue
                      let timestamp = listOne.TimeStamp
                      where listOne.TimeStamp == listTwo.TimeStamp
                      select new {ColumnFromListTwo = columnFromListOne, ColumnFromListOne = columnFromListTwo, Timestamp = timestamp});


         foreach(var q in query)
            dataTable.Rows.Add(q.ColumnFromListOne, q.ColumnFromListTwo, q.TimeStamp);

         return dataTable;
      }

The problem is the two lists contain timestamps that are off by a matter of seconds, and they don’t align at all, so my end result ends up with one or zero records in the datatable, even though each list contains 200+ records. I’m pretty bad with LINQ and would appreciate a point in the right direction. I guess I need to interpolate the timestamps before grouping, but I would like to know the best practice pattern for doing something like this.

Answer 1

You need to decide what an appropriate threshold is for calling two time stamps “equal” – knowing that too large a threshold will give you false positives and too small a threshold will prevent some records from joining.

From there just change your query to

     int threshold = 5;
     //Group the lists together
     var query = (from listOne in listOneDataValues
                  from listTwo in listTwoDataValues
                  where Math.Abs(
                                    (listOne.TimeStamp - listTwo.TimeStamp)
                                     .TotalSeconds
                                ) <= threshold
                  select new {
                                 ColumnFromListTwo = listTwo.DoubleValue,
                                 ColumnFromListOne = listOne.DoubleValue, 
                                 Timestamp = listOne.TimeStamp
                             });