How make lambda where on list of list?

Question

I have two classes:

public class firstClass
{
    public int Id { get; set; }
    public List<secondClass> Elements { get; set; }
}

public class secondClass
{
    public int Id { get; set; }
    public bool Is{ get; set; }
}

and using of their:

List<firstClass> list = allFirstClassFromDB.Include("Elements");

and then my list contain for example:

list[0] - {Id : 1, Elements : [0] { Id: 1, Is: true }, [1] { Id: 2, Is: true }, [2] { Id: 3, Is: false }
list[1] - {Id : 2, Elements : [0] { Id:4, Is: false }, [1] { Id: 5, Is: true }, [2] { Id: 6, Is: false }
list[2] - {Id : 3, Elements : [0] { Id:7, Is: false } }

So The result which I need is only this location which contain Elements which have Is prop set for true, sth like this:

list[0] - {Id : 1, Elements : [0] { Id: 1, Is: true }, [1] { Id: 2, Is: true } }
list[1] - {Id : 2, Elements : [0] { Id: 5, Is: true } }

It is possible in linq? Any help would be appreciated.

Martin Liversage · Accepted Answer · 2012-09-26 07:17:42Z

4

Here is how you can do it using LINQ:

var filteredList = list
  .Select(
    x => new firstClass {
      Id = x.Id,
      Elements = x.Elements.Where(y => y.Is).ToList()
    }
  )
  .Where(x => x.Elements.Count > 0);

answered Sep 26, 2012 at 7:17

Martin Liversage

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Comments

cuongle · Accepted Answer · 2012-09-26 07:27:35Z

1

First, get rid of firstClass which does not have any secondClass.Is true by Where clause, then re-build firstClass just to filter all secondClass.Is true

list.Where(f => f.Elements.Any(s => s.Is))
    .Select(f => new firstClass() {
                                      Id = f.Id,
                                      Elements = f.Elements.Where(s => s.Is)
                                                           .ToList()
    }).ToList();

edited Sep 26, 2012 at 7:27

answered Sep 26, 2012 at 7:21

cuongle

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