LINQ Grouping by

Question

I have list of class objects similar

 public class MyClass
    {
        public int UserId { get; set; }
        public int ItemId { get; set; }
        public string ItemName { get; set; }
    }

I have list of this, where I want to group them by UserId. Result I am after is sets of List<MyClass> where each list is by user

I have applied the group by but not sure how the select should be

  var group = items.GroupBy(g => g.UserId).
                Select(s=> new MyClass { 
                UserId = s.Key,
              
                }).ToList();

Sample data

  var items = new List<MyClass>
            {
                new MyClass{UserId = 100, ItemId = 245, ItemName = "ABC"},
                new MyClass{UserId = 100, ItemId = 125, ItemName = "ABCff"},
                new MyClass{UserId = 150, ItemId = 233, ItemName = "AweBC"},
                new MyClass{UserId = 100, ItemId = 233, ItemName = "ABweweC"}
            };

Here I would expect two sets of List<MyClass> one list with userid 100 and other with 150 and each list will have 2 class objects

then you can Order current `items` by `UserId` so that all your records with the same UserId will be at the same group — Sowmyadhar Gourishetty, Aug 11 '20 at 12:06
I have updated question with sample data and expected result — user12073359, Aug 11 '20 at 12:08
I will also recommend a quick look at the example in the [MSDN](https://learn.microsoft.com/en-us/dotnet/api/system.linq.enumerable.groupby?view=netcore-3.1). Here grouping return an already grouped result `items.GroupBy(g => g.UserId).ToList()` https://dotnetfiddle.net/CmWnd8 — Drag and Drop, Aug 11 '20 at 12:13
Please [edit] your question with an example of what the outcome data structure should be. — Heretic Monkey, Aug 11 '20 at 12:15

score 2 · Answer 1 · answered Aug 11 '20 at 12:11

You can create a dictionary with UserId as it's key:

var groups = items.GroupBy(c => c.UserId)
                  .ToDictionary(g => g.Key, g => g.ToList());

Now for example, the following:

 Console.WriteLine(String.Join(Environment.NewLine, groups[100]));

Will print out:

100 245 ABC
100 125 ABCff
100 233 ABweweC

score 1 · Accepted Answer · answered Aug 11 '20 at 12:15

1

I think you are after this which will give you List<List<MyClass>>

var group = items.GroupBy(g => g.UserId).Select(s => s.ToList());

answered Aug 11 '20 at 12:15

huMpty duMpty

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That's IEnumerable>, right? Missing a ToList – Drag and Drop Aug 11 '20 at 12:19
1

I think you get the idea is it – huMpty duMpty Aug 11 '20 at 12:20
exactly what i was after – user12073359 Aug 11 '20 at 12:21

LINQ Grouping by

2 Answers2