Clever Geek Handbook

Using List <Person> Distinct () to return 2 values

I have a class Person

with properties Name

and AreaID

.

public class Person
{
   public string Name;
   public int AreaID;

   // snip
}

I have List<Person>

with potential for hundreds of Person objects in a list. e.g. 100 people with AreaID = 1 and 100 people with AreaID = 2

I want to return a separate list of AreaIDs and how many people have that AreaID.

For example, AreaID = 1 person. = 100 AreaID = 2 people = 100

+2


source to share


10 replies


It sounds like you want to group by area ID:

var groups = from person in persons
             group 1 by person.AreaID into area
             select new { AreaID = area.Key, Persons = area.Count() };


I use "group 1" to indicate that I don't really care about the data in each group - just the account and key.

It's inefficient in that it has to buffer all the results for grouping - you should be fine with using Reactive LINQ in .NET 4.0 to do this more efficiently, or you can certainly use push LINQ if you like. Again, for relatively small datasets this probably doesn't matter :)

+5


source


Use the GroupBy method.



var list = ...list of Persons...

var areas = list.GroupBy( p => p.AreaID )
                .Select( g => new {
                    AreaID = g.Key,
                    Count = g.Count()
                 });
+6


source


Unexpectedly, no one recommended canceling Equals

and GetHashCode

. If you do, you can do the following:

 List<Person> unique = personList.Distinct();

Or even

 List<Person> areaGroup = personList.GroupBy(p => p.AreaID);
 List<Person> area1Count = personList.Where(p => p.AreaID == 1).Count();

This gives you more flexibility - no need for a useless anonymous class.

+1


source 


return list.GroupBy(p => p.AreaID)
    .Select(g => new { AreaID = g.Key, People = g.Count() });
0


source


Instead of using it alone, use GroupBy or the more succinct LINQ operator:

var results = from p in PersonList
              group p by p.AreaID into g
              select new { AreaID=g.Key, Count=g.Count() };

foreach(var item in results)
    Console.WriteLine("There were {0} items in Area {1}", item.Count, item.AreaID);
0


source


you can use list.GroupBy(x => x.AreaID);

0


source


You can try this:

var groups = from person in list
             group person by person.AreaID into areaGroup
             select new {
                 AreaID = areaGroup.Key,
                 Count = areaGroup.Count()
             };
0


source 


        var people = new List<Person>();

        var q = from p in people
                group p by p.AreaId into g
                select new { Id = g.Key, Total = g.Count() };


        people.Add(new Person { AreaId = 1, Name = "Alex" });
        people.Add(new Person { AreaId = 1, Name = "Alex" });
        people.Add(new Person { AreaId = 2, Name = "Alex" });
        people.Add(new Person { AreaId = 3, Name = "Alex" });
        people.Add(new Person { AreaId = 3, Name = "Alex" });
        people.Add(new Person { AreaId = 4, Name = "Alex" });
        people.Add(new Person { AreaId = 2, Name = "Alex" });
        people.Add(new Person { AreaId = 4, Name = "Alex" });
        people.Add(new Person { AreaId = 1, Name = "Alex" });

        foreach (var item in q)
        {
            Console.WriteLine("AreaId: {0}, Total: {1}",item.Id,item.Total);
        }
0


source


Something like this, perhaps?

            List<Person> persons = new List<Person> ();
            persons.Add (new Person (1, "test1"));
            persons.Add (new Person (1, "test2"));
            persons.Add (new Person (2, "test3"));

            var results = 
                persons.GroupBy (p => p.AreaId);

            foreach( var r in results )
            {
                Console.WriteLine (String.Format ("Area Id: {0} - Number of members: {1}", r.Key, r.Count ()));
            }

            Console.ReadLine ();
0


source


ToLookup()

will do what you want.

0


source






More articles:


All Articles