Select Distinct Values from C# List

Question

_{Sunday, November 26, 2017 3:09 PM}

I have the following below Linq Statement which I use to select how many Value I have in a list myList

        class MyClassDetails
        {
            public string ID;
            public int Value;
        }

        class MyClass
        {
            public MyClass()
            {
                moreDetails = new ObservableCollection<MyClassDetails>();
            }
            public string Name;
            public ObservableCollection<MyClassDetails> moreDetails;
        }

        static void Main(string[] args)
        {
            var myList = new List<MyClass>();

            var myClass1 = new MyClass();
            myClass1.Name = "Class1";
            myClass1.moreDetails.Add(new MyClassDetails() { Value = 1, ID="ONE" });
            myClass1.moreDetails.Add(new MyClassDetails() { Value = 2, ID = "TWO" });
            myClass1.moreDetails.Add(new MyClassDetails() { Value = 4, ID = "ONE" });
            myClass1.moreDetails.Add(new MyClassDetails() { Value = 8, ID = "TWO" });
            myClass1.moreDetails.Add(new MyClassDetails() { Value = 16, ID = "ONE" });

            var myClass2 = new MyClass();
            myClass2.Name = "Class2";
            myClass2.moreDetails.Add(new MyClassDetails() { Value = 1, ID = "TWO" });
            myClass2.moreDetails.Add(new MyClassDetails() { Value = 2, ID = "ONE" });
            myClass2.moreDetails.Add(new MyClassDetails() { Value = 4, ID = "ONE" });
            myClass2.moreDetails.Add(new MyClassDetails() { Value = 8, ID = "TWO" });
            myClass2.moreDetails.Add(new MyClassDetails() { Value = 54, ID = "ONE" });

            myList.Add(myClass1);
            myList.Add(myClass2);

            var groups2 = myList.SelectMany(myClass => myClass.moreDetails, (myClass, details) => new { details.Value, myClass.moreDetails })
                                .GroupBy(myClass => myClass.Value)
                                .Select(g => new { Value = g.Key, Count = g.ToList().Distinct().Count() });


            foreach (var group in groups2)
            {
                var value = group.Value;                var count = group.Count;
            }

So the above will output the following:

group1: Value 1 Count 2

group2: Value 2 Count 2

group3: Value 4 Count 2

group4: Value 8 Count 2

group5: Value 54 Count 1

I want to only count the Distinct Values by ID

So for the above the groups 3 and 4 would only have count=1 as they have the same ID values

group3: Value 4 Count 1

group4: Value 8 Count 1

How do I modify my query to do this?

All replies (2)

_{Sunday, November 26, 2017 4:47 PM | 1 vote}

Try this:

var groups3 = myList
                 .SelectMany( c => c.moreDetails )
                 .GroupBy( d => d.Value )
                 .Select( g => new { Value = g.Key, Count = g.GroupBy( d => d.ID ).Count() } );

and this:

var groups4 = myList
                 .SelectMany( c => c.moreDetails )
                 .GroupBy( d => d.Value, ( k, e ) => new { Value = k, Count = e.GroupBy( d => d.ID ).Count() } );

_{Tuesday, November 28, 2017 12:17 PM}

Hello LearnerMan1234,

Try the below code. There is a way via using "groupby" statement twice. The first group by the "id" and "value". The second group by "value" based on the first result.

  var result = myList.SelectMany(MyClass => MyClass.moreDetails)
                .GroupBy(x => new { Id = x.ID, Value = x.Value }).GroupBy(j => j.Key.Value)
                .Select(z => new { value = z.Key, Count = z.Count() }).ToList();

And the linq could be separated by some parts as below. This can be beneficial to debug.

 var step1 = myList.SelectMany(myClass => myClass.moreDetails, (myClass, details) => new { details.Value, details.ID }).ToList();

            var step2 = step1.GroupBy(x => new{ Id= x.ID, Value=x.Value});

            var step3 = step2.Select(g =>new {value=g.Key.Value}).ToList();

            var step4 = step3.GroupBy(j =>j.value);

            var step5=step4.Select(z=>new { value=z.Key,Count=z.Count()}).ToList();

Best regards,

Neil Hu

MSDN Community Support
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