get only latest items for each id type

Question

I have a collection of objects and i need to retreive the ones that were last created for the same type(similar ids). I tried the idea below from an other post but i do not get the expected result. Any other suggestions?

Thanks in advance

void Main()
{
List<data_item> itemlist1= new List<data_item>();


itemlist1.Add(new UserQuery.data_item 
{
 id=1,

   Creationdate = new DateTime(2001, 6, 1),
    Size=28373

})
;
itemlist1.Add(new UserQuery.data_item 
{
 id=2,

   Creationdate = new DateTime(1992, 6, 1),
    Size=2000

})
;

itemlist1.Add(new UserQuery.data_item 
{
 id=2,


    Creationdate = new DateTime(2002, 6, 1),
     Size=300
})
;
itemlist1.Add(new UserQuery.data_item 
{
 id=1,


   Creationdate = new DateTime(2005, 6, 1),
   Size =400
})
;
itemlist1.Add(new UserQuery.data_item 
{
 id=3,


  Creationdate = new DateTime(1999, 6, 1),
  Size =10000
})
;
itemlist1.Add(new UserQuery.data_item 
{
 id=3,


  Creationdate = new DateTime(2003, 6, 1),
  Size =5000
})
;
itemlist1.Add(new UserQuery.data_item 
{
 id=3,


  Creationdate = new DateTime(1999, 4, 1),
  Size=3000
})
;
itemlist1.Add(new UserQuery.data_item 
{
 id=5,


  Creationdate = new DateTime(1999, 6, 5),
  Size=230
})
;
itemlist1.Add(new UserQuery.data_item 
{
 id=4,

  Creationdate = new DateTime(1999, 6, 1),
  Size =8700
})
;
itemlist1.Add(new UserQuery.data_item 
{
 id=5,


  Creationdate = new DateTime(1991, 6, 1),
  Size =6000
})
;

itemlist1.Dump();



var result = from t in itemlist1 group t by new UserQuery.data_item 
{ id=t.id,
Creationdate=t.Creationdate
} into gt

select gt.OrderByDescending(d=>d.Creationdate).First();

result.Distinct().Dump();
}

// Define other methods and classes here

public class data_item
{
 public int id {get;set;}

 public DateTime Creationdate {get;set;}
 public int? Size {get;set;}



 }

Answer 1

Is this what you need?

var group = itemlist1.GroupBy(x=>x.id); // grouped by id
var newList = 
      group.Select(g => g.OrderByDescending(y => y.Creationdate).First());

it will get most recent items for all ids, by grouping them by ID and then taking only most recent ones from that list and selecting to new list

OrderByDescending is ordering by date descending so First is taking most recent date. Select is selecting expression result to new list, so there should be a list of most recent items for all id's groups