Trouble with linq/GroupBy/Count

Question

I have the following data set:

vehicleid   elapsedTimeLastConnection   timestampLastConnection     avgConnectionDuration
20472       1054471                     2021-04-01 08:45:29.000     195
20400       1048824                     2021-04-01 10:19:36.777     2522
20464       1048764                     2021-04-01 10:20:36.000     1065
26235       1042766                     2021-04-01 12:00:34.000     1028
20472       1029448                     2021-04-01 15:42:32.000     1168
20464       983912                      2021-04-02 04:21:28.777     37
20417       974218                      2021-04-02 07:03:02.000     15031
20422       966875                      2021-04-02 09:05:25.777     3
20422       962542                      2021-04-02 10:17:38.777     2922
26235       961541                      2021-04-02 10:34:19.000     1137
20464       961189                      2021-04-02 10:40:11.000     5362
20472       939075                      2021-04-02 16:48:45.777     763
20473       931086                      2021-04-02 19:01:54.777     3428
20472       885385                      2021-04-03 07:43:35.000     1683
20412       878456                      2021-04-03 09:39:04.777     1601
20400       875267                      2021-04-03 10:32:13.000     322
20398       871287                      2021-04-03 11:38:33.777     1035
26235       863747                      2021-04-03 13:44:13.000     1322
20400       845021                      2021-04-03 18:56:19.000     2471
20410       811539                      2021-04-04 04:14:21.777     1
20410       801662                      2021-04-04 06:58:58.000     1403
20424       787282                      2021-04-04 10:58:38.777     220
20472       783425                      2021-04-04 12:02:55.777     1010
26235       777413                      2021-04-04 13:43:07.000     971
20451       776365                      2021-04-04 14:00:35.777     30
20422       774753                      2021-04-04 14:27:27.777     10
20451       774458                      2021-04-04 14:32:22.000     0
20422       770654                      2021-04-04 15:35:46.777     199
20424       768515                      2021-04-04 16:11:25.777     158
20424       758100                      2021-04-04 19:05:00.777     3420
20422       757804                      2021-04-04 19:09:56.777     1974
26431       749178                      2021-04-04 21:33:42.777     3
26431       744800                      2021-04-04 22:46:40.777     1
26431       743230                      2021-04-04 23:12:50.777     3
20473       725451                      2021-04-05 04:09:09.000     1
26431       724816                      2021-04-05 04:19:44.777     47
20473       724478                      2021-04-05 04:25:22.777     2232
20472       722822                      2021-04-05 04:52:58.000     1
26431       716665                      2021-04-05 06:35:35.777     258
20410       714575                      2021-04-05 07:10:25.777     1750
26235       705768                      2021-04-05 09:37:12.000     440
20472       705134                      2021-04-05 09:47:46.777     1576
26431       693675                      2021-04-05 12:58:45.000     1
20398       677341                      2021-04-05 17:30:59.000     3688
26431       676935                      2021-04-05 17:37:45.000     1
26431       676014                      2021-04-05 17:53:06.777     1075
26235       674789                      2021-04-05 18:13:31.777     7
26235       673755                      2021-04-05 18:30:45.000     802
20400       671561                      2021-04-05 19:07:19.777     529
20464       634465                      2021-04-06 05:25:35.777     1
20400       627857                      2021-04-06 07:15:43.777     1274
26235       623214                      2021-04-06 08:33:06.000     2679
20422       621451                      2021-04-06 09:02:29.777     1
20422       620461                      2021-04-06 09:18:59.777     4185
20464       611819                      2021-04-06 11:43:01.777     1021
26431       611458                      2021-04-06 11:49:02.000     1446
20472       609710                      2021-04-06 12:18:10.777     1360
20410       600170                      2021-04-06 14:57:10.777     12
20410       589821                      2021-04-06 17:49:39.777     610
20473       585735                      2021-04-06 18:57:45.000     1004
20451       583418                      2021-04-06 19:36:22.777     2

I'm grouping by day of week with the following linq query:

var toBeReturned = dataSet
  .GroupBy(row => new DateTime(row.timestampLastConnection.Ticks).ToLocalTime().DayOfWeek);

Which gives me exactly what I want. So far so good.

Now I want to count the distinct vehicleIds per group, so I ended up with:

var toBeReturned2 = toBeReturned
    .Select(g =>
    {
        int vCount = g.Select(c => c.vehicleId).Distinct().Count();
        return new
        {
            DayOfWeek = g.Key,
            count = vCount,
            duration = g.Average(c => c.avgConnectionDuration) / vCount
        };
    });

The problem is that vCount is always 1 instead of beeing the count of distinct vehicleIds for the selected group.

{ DayOfWeek = Thursday, count = 1, duration = 997.90909090909088 }
{ DayOfWeek = Friday, count = 1, duration = 2124.2380952380954 }
{ DayOfWeek = Saturday, count = 1, duration = 1329.1666666666667 }
{ DayOfWeek = Sunday, count = 1, duration = 657.05882352941171 }
{ DayOfWeek = Monday, count = 1, duration = 642 }
{ DayOfWeek = Tuesday, count = 1, duration = 1132.9166666666667 }
{ DayOfWeek = Wednesday, count = 1, duration = 891.81818181818187 }

What Am I doing wrong?

Answer 1

Try narrowing the problem down. If you remove .Distinct() does it return the full count of each group? If so, maybe the issue is the contents of your vehicleId column.

Per comment: the field isn't being deserialized into the object (wrong name) and so all the values are null or empty and they are thus not distinct.

Answer 2

Try following code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO;
using System.Data;

namespace ConsoleApplication187
{
    class Program
    {
        const string FILENAME = @"c:\temp\test.txt";
        static void Main(string[] args)
        {
            DataTable dt = new DataTable();
            dt.Columns.Add("vehicleid", typeof(int));
            dt.Columns.Add("elapsedTimeLastConnection", typeof(long));
            dt.Columns.Add("timestampLastConnection", typeof(DateTime));
            dt.Columns.Add("avgConnectionDuration", typeof(long));

            int col1Len = "vehicleid   ".Length;
            int col2Len = "elapsedTimeLastConnection   ".Length;
            int col3Len = "timestampLastConnection     ".Length;
            int col4Len = "avgConnectionDuratio".Length;

            StreamReader reader = new StreamReader(FILENAME);
            string line = "";
            int rowCount = 0;
            while((line = reader.ReadLine()) != null)
            {
                if (++rowCount > 1)
                {
                    dt.Rows.Add(new object[] {
                        int.Parse(line.Substring(0,col1Len)),
                        long.Parse(line.Substring(col1Len,col2Len)),
                        DateTime.Parse(line.Substring(col1Len + col2Len,col3Len)),
                        long.Parse(line.Substring(col1Len + col2Len + col3Len))
                    });
                }
            }
            var toBeReturned = dt.AsEnumerable().GroupBy(row => row.Field<DateTime>("timestampLastConnection").ToLocalTime().DayOfWeek);
            var toBeReturned2 = toBeReturned.OrderBy(x => x.Key).Select(x => new { key = x.Key, count = x.Count() }).ToList();

        }
    }
}

Answer 3

One possible answer is that your vehicleId is not fetched and defaulted to 0 or null .