C# count ocurrences in each date using Linq

Question

I have a list of objects like this:

public class Entity
{
    public int Id { get; set; }
    public DateTime Date { get; set; }
}

| Id | Date                | 
| 1  | 2017-01-16 12:58:32 |
| 2  | 2017-01-16 11:36:01 |
| 3  | 2017-01-16 17:55:19 |
| 4  | 2017-01-19 13:19:40 |
| 5  | 2017-01-19 09:21:55 |

And I would like to filter this using LINQ to count the number of ocurrences by day. So the result would be something like this:

| Date       | Occurrences |
| 2017-01-16 |   3         | 
| 2017-01-17 |   2         |

Is it possible to do this with LINQ?

you want GroupBy

Jonesopolis
– Jonesopolis

2017-04-14 17:52:48 +00:00
Commented Apr 14, 2017 at 17:52 — Jonesopolis
– Jonesopolis, Commented Apr 14, 2017 at 17:52

Igor · Accepted Answer · 2017-04-14 17:54:06Z

6

You want to use GroupBy

var lst = new List<Entity>(); // populate with your data
var result = lst
    .GroupBy(x => x.Date.Date, x => x.Id)
    .Select(x => new { Date = x.Key, Occurrences = x.Count() });

answered Apr 14, 2017 at 17:54

Igor

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Comments

jdweng · Accepted Answer · 2017-04-14 17:59:31Z

Try something like this

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO;
using System.Data;
using System.Xml;
using System.Xml.Linq;



namespace ConsoleApplication49
{
    class Program
    {

        static void Main(string[] args)
        {
            List<Entity> entities = new List<Entity>() {
                new Entity() { Id = 1, Date = DateTime.Parse("2017-01-16 12:58:32")},
                new Entity() { Id = 2, Date = DateTime.Parse("2017-01-16 11:36:01")},
                new Entity() { Id = 3, Date = DateTime.Parse("2017-01-16 17:55:19")},
                new Entity() { Id = 4, Date = DateTime.Parse("2017-01-19 13:19:40")},
                new Entity() { Id = 5, Date = DateTime.Parse("2017-01-19 09:21:55")}
            };

            var results = entities.GroupBy(x => x.Date.Date).Select(x => new { count = x.Count(), entities = x.ToList() }).ToList();
        }


    }
    public class Entity
    {
        public int Id { get; set; }
        public DateTime Date { get; set; }
    }



}

Eldar Kersebaum · Accepted Answer · 2017-04-14 21:42:14Z

Here are two Solutions:

1. The first uses LINQ to query entities.

2. The second make use of multiple LINQ functions to group and count entities.

using System;
using System.Collections.Generic;
using System.Linq;

namespace LinqExample
{
    class Program
    {
        public class Entity
        {
            public int Id { get; set; }
            public DateTime Date { get; set; }
        }
        static void Main(string[] args)
        {
            List<Entity> entities = new List<Entity>()
            {
                new Entity() { Id = 1, Date = DateTime.Parse("2017-04-14 21:02:37")},
                new Entity() { Id = 2, Date = DateTime.Parse("2017-04-14 21:03:42")},
            };

            var OccurencesPerDay = from entity in entities
                                   group entity by entity.Date.Date into g
                                   select new {Date = g.Key.Date, Occurences = g.Count()};
            // Above is more readable than, even though both are equal
            OccurencesPerDay = entities.
                GroupBy(ent => ent.Date.Date).
                Select(ents => new { Date = ents.Key.Date, Occurences = ents.Count()} );



            Console.WriteLine($"| Date | Occurences |");
            foreach (var occ in OccurencesPerDay)
            {
                Console.WriteLine($"| {occ.Date} | {occ.Occurences} |");
            }
        }
    }
}

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C# count ocurrences in each date using Linq

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1. The first uses LINQ to query entities.

2. The second make use of multiple LINQ functions to group and count entities.

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3 Answers 3

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1. The first uses LINQ to query entities.

2. The second make use of multiple LINQ functions to group and count entities.

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