Group DateTime List By Date using LINQ

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Hello CPians,

I am sharing the problem, which I am facing while grouping the DateTime List by Date.

The code is like below...

C#

List<DateTime> slotsAvailable = new List<DateTime>();

// Then I did some operations and added some DateTime to this list and now sorting it.
slotsAvailable.Sort();

// Here I am Grouping the List.
var grouppedResult = slotsAvailable.GroupBy(x => x.Date);

Problem
When I am grouping the DateTime List by Date, one Group can contain maximum 18 number of DateTimes.

For Example - DateTime are like "18/05/2013 11:00:00 AM" .... "18/05/2013 07:30:00 PM".
Now, when I group by Date that is by "18/05/2013", then the group should contain 18 number of elements starting from "18/05/2013 11:00:00 AM", "18/05/2013 11:30:00 AM" up to "18/05/2013 07:30:00 PM" with a interval of 30 minutes.

But I am getting many default DateTime added to this group after the 18th element.

You can see in the image - Group DateTime List By Date using LINQ[^], where I added the debugged result.

In the image, you can check that after the [17] position in the elements group, there are many default DateTime added like "01/01/0001 12:00:00 AM".

Please explain what is the problem and how to solve it.

Thanks,
Tadit

Posted 17-May-13 18:46pm

Tadit Dash (ତଡିତ୍ କୁମାର ଦାଶ)

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walterhevedeich 23-May-13 3:16am

Did you try checking the contents of slotsAvailable even before the group? Maybe those dates were already in there in the first place.

Tadit Dash (ତଡିତ୍ କୁମାର ଦାଶ) 23-May-13 3:57am

Yes, I have checked.
Initially they are not present, but after I group them, they are getting added.

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Tadit Dash (ତଡିତ୍ କୁମାର ଦାଶ) · Accepted Answer · 2013-05-29T00:41:00

Finally I came up with a similar solution as suggested by @David in Solution 1 to remove the null ones. Posting it now after he gave the solution.

He is comparing like below.
m.Date.ToShortDateString() != "1/1/0001"

I compared with DateTime.MinValue. So, my code is like below.

C#

// Other logic to Remove the duplicate DateTimes.
var distinctResult = slotsAvailable.GroupBy(x => x.ToString()).Select(y => y.First()).ToList();

distinctResult.Sort();

// Logic to Group By Date.
var distinctGroupedResultByDate = distinctResult.GroupBy(x => x.Date);

// Remove the null or <code>DateTime</code> which has <code>MinValue</code>.
var finalAvailableSlots = from q in distinctGroupedResultByDate
                          where q.ToString() != DateTime.MinValue.ToString()
                          select q.ToList();

David_Wimbley · Accepted Answer · 2013-05-28T12:49:00

Hey Tadit,

From what i can tell, the reason why your getting "null" date times in your collection is because whatever class your collection of slotsAvailable is...does not have values for those datetimes.

Here is a recreation of your problem...piping the group by output to Console.WriteLine.

C#

public static void Q594720()
{
   List<Slots> slotsAvailable = new List<Slots>();
   slotsAvailable.Add(new Slots { Name = "Class 1", Date = DateTime.Now.AddDays(1) });
   slotsAvailable.Add(new Slots { Name = "Class 2", Date = DateTime.Now.AddDays(2) });
   slotsAvailable.Add(new Slots { Name = "Class 3", Date = DateTime.Now.AddDays(3) });
   slotsAvailable.Add(new Slots { Name = "Class 4", Date = DateTime.Now.AddDays(4) });
   slotsAvailable.Add(new Slots { Name = "Class 5" });
   slotsAvailable.Add(new Slots { Name = "Class 6" });
   slotsAvailable.Add(new Slots { Name = "Class 7" });
   slotsAvailable.Add(new Slots { Name = "Class 8" });


   foreach (var items in slotsAvailable.GroupBy(m => m.Date).ToList())
   {
      foreach (var slotse in items)
      {
         Console.WriteLine("Date Value:" + slotse.Date.ToString());   
      }
   }
}

public class Slots
{
   public string Name {get;set;}
   public DateTime Date {get;set;}
}

A quick and dirty fix for this would be to add a .Where to your .GroupBy that says Where Date != "1/1/0001".

C#

foreach (var items in slotsAvailable.Where(m=>m.Date.ToShortDateString() != "1/1/0001").GroupBy(m => m.Date).ToList())
{
   foreach (var slotse in items)
   {
      Console.WriteLine("Date Value:" + slotse.Date.ToString());   
   }
}

Group DateTime List By Date using LINQ

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Solution 1

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