How do group by and count in lambda expression

Question

1.00/5 (1 vote)

See more:

I have one model
MaterialModel

ID Material
1 MaterialZZZ
2 MaterialYYY
3 MaterialXXX
1 MaterialABC
2 MaterialKKK
2 MaterialVVV
5 MaterialMMM

Expected Result (Result Model)
ID Count
1 2
2 3
3 1
5 1
I want to group by and take the count and ID in linq lambda expression and that result to another List of Model. which has ID and Count properties

What I have tried:

int count = (from x in items select x).Count();

but i need group by and count in another list of model.

Thanks in advance.

Posted 14-Mar-22 8:06am

Salt Pepper

Updated 14-Mar-22 10:48am

Add a Solution

2 solutions

Solution 2

Take a look at below code:

void Main()
{
	List<MaterialModel> mm = new List<MaterialModel>()
	{
		new MaterialModel(){ID = 1, Material = "MaterialZZZ"},
		new MaterialModel(){ID = 2, Material = "MaterialYYY"},
		new MaterialModel(){ID = 3, Material = "MaterialXXX"},
		new MaterialModel(){ID = 1, Material = "MaterialABC"},
		new MaterialModel(){ID = 2, Material = "MaterialKKK"},
		new MaterialModel(){ID = 2, Material = "MaterialVVV"},
		new MaterialModel(){ID = 5, Material = "MaterialMMM"}	
	};

	List<ResultModel> rm = mm.GroupBy(x => x.ID)
		.Select(grp => new ResultModel()
		{
			ID = grp.Key,
			Count = grp.Count()
		})
		.ToList();
	rm.Dump();
}

// Define other methods and classes here
public class MaterialModel
{
	public int ID { get; set; }	
	public string Material { get; set; }
}

public class ResultModel
{
	public int ID { get; set; }
	public int Count { get; set; }
}

Next time, i'd suggest to read MSDN documentation first:
Group query results (LINQ in C#) | Microsoft Docs[^]
Enumerable.GroupBy Method (System.Linq) | Microsoft Docs[^]
101 LINQ samples - Code Samples | Microsoft Docs[^]

Posted 14-Mar-22 10:48am

Maciej Los

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Luc Pattyn · Accepted Answer · 2022-03-14T08:29:00

static void Main(string[] args) {
    List<Item> items=new List<Item>();
    items.Add(new Item(1, "zzz"));
    items.Add(new Item(2, "yyy"));
    items.Add(new Item(3, "xxx"));
    items.Add(new Item(1, "abc"));
    items.Add(new Item(2, "kkk"));
    items.Add(new Item(2, "bbb"));
    items.Add(new Item(5, "mmm"));
    var counters = from r in items
                  group r by r.ID into grp
                  select new { key = grp.Key, cnt = grp.Count() };
    foreach (var counter in counters) {
        Console.WriteLine("key=" + counter.key + ", count=" + counter.cnt);
    }

or

...
	var counters = items.GroupBy(r => r.ID)
		.Select(group => new { key = group.Key, cnt = group.Count() });
...

both with

public class Item {
    public int ID { get; set; }
    public string Material { get; set; }
    public Item(int ID, string material) {
        this.ID = ID;
        this.Material = material;
    }
}