Solved

Using Linq to filter collection with group By and select max

Posted on 2009-07-14
3
3,034 Views
Last Modified: 2013-11-11
Given the sample code shown below, how can I use linq to filter the collection to group By field1 and select the highest value of field2, so that my new collection would have classB and classC only in it?
public class Class1

    {

        public int field1;

        public int field2;

        public DateTime field3;

        public int field4;

    }
 

    public class Class1Collection : Collection<Class1>, IEnumerable<Class1>

    {

    }
 
 

    public static class TestClass

    {
 

        public static void Test()

        {

            Class1 classA = new Class1();

            classA.field1 = 1;

            classA.field2 = 2;

            classA.field3 = new DateTime(2009, 01, 01);

            classA.field4 = 3;
 

            Class1 classB = new Class1();

            classB.field1 = 1;

            classB.field2 = 3;

            classB.field3 = new DateTime(2009, 02, 01);

            classB.field4 = 3;
 

            Class1 classC = new Class1();

            classC.field1 = 2;

            classC.field2 = 1;

            classC.field3 = new DateTime(2009, 02, 01);

            classC.field4 = 3;
 

            Class1Collection collection = new Class1Collection();

            collection.Add(classA);

            collection.Add(classB);

            collection.Add(classC);
 

            Class1Collection filteredCollection = ??

        }
 

    }

Open in new window

0
Comment
Question by:weimha
3 Comments
 
LVL 21

Assisted Solution

by:Craig Wagner
Craig Wagner earned 50 total points
ID: 24851703
Try this LINQ query...
from c in collection

group c by c.field1 into grouped

from g in grouped

where g.field2 == grouped.Max( m => m.field2 )

select g;

Open in new window

0
 
LVL 62

Assisted Solution

by:Fernando Soto
Fernando Soto earned 50 total points
ID: 24851753
Hi weimha;

Here is some sample code showing how this can be done.

Fernando
using System;

using System.Collections.Generic;

using System.ComponentModel;

using System.Data;

using System.Drawing;

using System.Linq;

using System.Text;

using System.Windows.Forms;
 

namespace WindowsFormsApplication45

{

    public partial class Form1 : Form

    {

        public Form1()

        {

            InitializeComponent();

        }
 

        List<Class1> collection = new List<Class1>();
 

        private void button1_Click(object sender, EventArgs e)

        {

            Class1 classA = new Class1();

            classA.field1 = 1;

            classA.field2 = 2;

            classA.field3 = new DateTime(2009, 01, 01);

            classA.field4 = 3;
 

            Class1 classB = new Class1();

            classB.field1 = 1;

            classB.field2 = 3;

            classB.field3 = new DateTime(2009, 02, 01);

            classB.field4 = 3;
 

            Class1 classC = new Class1();

            classC.field1 = 2;

            classC.field2 = 1;

            classC.field3 = new DateTime(2009, 02, 01);

            classC.field4 = 3;
 

            collection.Add(classA);

            collection.Add(classB);

            collection.Add(classC);
 

            List<Class1> filteredCollection = (from c in collection

                                               group c by c.field1 into classGroup

                                               let max = classGroup.Max(m => m.field2)

                                               from m in classGroup

                                               where m.field2 == max

                                               select m).ToList();
 

            // Display the results

            foreach (Class1 c1 in filteredCollection)

            {

                Console.WriteLine("{0,4}{1,4}{2,24}{3,4}",

                    c1.field1, c1.field2, c1.field3, c1.field4);

            }
 

        }

    }
 

    public class Class1

    {

        public int field1;

        public int field2;

        public DateTime field3;

        public int field4;

    }

}

Open in new window

0
 
LVL 15

Accepted Solution

by:
jinal earned 400 total points
ID: 24851810

public class Class1

    {

        public int field1;

        public int field2;

        public DateTime field3;

        public int field4;

    }
 

    public class Class1Collection : Collection<Class1>, IEnumerable<Class1> , IList<Class1>

    {

    }
 
 

    public static class TestClass

    {
 

        public static void Test()

        {

            Class1 classA = new Class1();

            classA.field1 = 1;

            classA.field2 = 2;

            classA.field3 = new DateTime(2009, 01, 01);

            classA.field4 = 3;

 

            Class1 classB = new Class1();

            classB.field1 = 1;

            classB.field2 = 3;

            classB.field3 = new DateTime(2009, 02, 01);

            classB.field4 = 3;

 

            Class1 classC = new Class1();

            classC.field1 = 2;

            classC.field2 = 1;

            classC.field3 = new DateTime(2009, 02, 01);

            classC.field4 = 3;

 

            Class1Collection collection = new Class1Collection();

            collection.Add(classA);

            collection.Add(classB);

            collection.Add(classC);
 
 

            IEnumerable<Class1> data =  from cc in collection 

                        join cc1 in (

                        from c in collection

                        group c by c.field1 into g

                        select new { ID = g.Key, Max = g.Max(p => p.field2) }) on cc.field1 equals cc1.ID  where cc.field2 == cc1.Max select cc;
 
 

            Class1Collection filtercollection = new Class1Collection();

            foreach (Class1 c in data)

            {

                filtercollection.Add(c);

            }

            

            

            
 

        }
 

    }

Open in new window

0

Featured Post

How to improve team productivity

Quip adds documents, spreadsheets, and tasklists to your Slack experience
- Elevate ideas to Quip docs
- Share Quip docs in Slack
- Get notified of changes to your docs
- Available on iOS/Android/Desktop/Web
- Online/Offline

Join & Write a Comment

Welcome my friends to the second instalment and follow-up to our Minify and Concatenate Your Scripts and Stylesheets (http://www.experts-exchange.com/Programming/Languages/.NET/ASP.NET/A_4334-Minify-and-Concatenate-Your-Scripts-and-Stylesheets.html)…
It was really hard time for me to get the understanding of Delegates in C#. I went through many websites and articles but I found them very clumsy. After going through those sites, I noted down the points in a easy way so here I am sharing that unde…
Get a first impression of how PRTG looks and learn how it works.   This video is a short introduction to PRTG, as an initial overview or as a quick start for new PRTG users.
When you create an app prototype with Adobe XD, you can insert system screens -- sharing or Control Center, for example -- with just a few clicks. This video shows you how. You can take the full course on Experts Exchange at http://bit.ly/XDcourse.

743 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

16 Experts available now in Live!

Get 1:1 Help Now