LINQ - filter collection inside collection

Question

Let's say I have the following classes:

class Parent
{
    bool Gender { get; set; }
    List<Child> Children { get; set; }
}


class Child
{
    bool Gender { get; set; }
    List<Child> GrandChildren { get; set; }
}


class GrandChild
{
    bool Gender { get; set; }
}

Using linq, can anyone help me filter a Parent object by returning a List<Child> where each Child has Gender == false and each Child's GrandChild has Gender == false?

I've managed to return a List<GrandChild> but I really need the hierarchy to be maintained.

Do you mean you *only* want the children to be returned where their gender is false and all their children have a gender of false? — Jon Skeet, Dec 27 '10 at 17:39
As a side note, I'd suggest you to change `Gender` property to Enum {Male,Female} because `Gender=true/false` is pretty unclear to understand... — digEmAll, Dec 27 '10 at 17:42
I love Gender being a bool. So is male represented by `true` and female by `false`? Like in real life? ;-P — Klaus Byskov Pedersen, Dec 27 '10 at 17:43
:) Gender was just an example.. thanks for all the quick answers — pedrodbsa, Dec 27 '10 at 17:52
Maybe i wasn't clear enough.. The queries do not filter the grandchildren.. they only return a list that have Gender==false GrandChild objects. But the GrandChildren collection still isn't filtered.. it still returns Gender == false and true GranChild — pedrodbsa, Dec 27 '10 at 17:59

score 17 · Answer 1 · answered Dec 27 '10 at 17:41

17

You're looking for

.Where(p => p.Children.All(c => !c.Gender && c.GrandChildren.All(g => !g.Gender))

answered Dec 27 '10 at 17:41

SLaks

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I want to filter out all the objects that have Gender == true but still maintain the same structure – pedrodbsa Dec 27 '10 at 18:01
@teknoplast: What do you mean? – SLaks Dec 27 '10 at 18:03
i want to filter both List and List so that Gender == false. with your code it returns a filtered List but the GrandChildren isn't being filtered – pedrodbsa Dec 27 '10 at 18:08
You'll need to clone your `Child` objects, then call `RemoveAll` on the clones' Lists to get rid of unwanted grandchildren. – SLaks Dec 27 '10 at 18:09
1

so why is this the accepted answer and not mine which does exactly this? :) – fejesjoco Dec 27 '10 at 18:19

fejesjoco · Accepted Answer · 2017-11-23T12:40:52.743

Your question is a bit vague. Here's a solution which rebuilds the children and grandchildren lists, I wasn't sure if I needed the child.GrandChildren.All(gc => !gc.Gender) so I left it out for clarity:

parents.Select(parent => new Parent
{
  Gender = parent.Gender,
  Children = parent.Children.Where(child => !child.Gender).Select(child => new Child
    {
      Gender = false,
      GrandChildren = child.GrandChildren.Where(gc => !gc.Gender).ToList()
    }
  ).ToList()
})

Amy B · Answer 3 · 2010-12-27T18:19:53.323

help me filter a Parent object
by returning a List<Child>
where each Child has Gender == false
and each Child's GrandChild has Gender == false?

Translated literally:

List<Child> results =
(
  from c in theParent.Children
  where !c.Gender
  where c.GrandChildren.Any(gc => !gc.Gender)
  select c
).ToList()

Based on your comments, what you really want:

List<Parent> result = 
(
from p in Parents
where !p.Gender
select new Parent()
{
  Gender = p.Gender,
  Children = 
  (
    from c in p.Children
    where !c.Gender
    select new Child()
    {
      Gender = c.Gender,
      GrandChildren =
      (
        from gc in c.GrandChildren
        where !gc.Gender
        select new GrandChild()
        {
          Gender = gc.Gender
        }
      ).ToList()
    }
  ).ToList()
}).ToList();

score 1 · Answer 4 · answered Dec 27 '10 at 17:40

var filteredParents = 
    from p in parents
    where p.Children.All(child => !child.Gender &&
                         child.GrandChildren.All(grandChild => !grandChild.Gender))
    select p;

Using All method here ensures that the predicate passed as an argument to that method is true for all elements in given sequence.

Given code checks for each parent that has All children with (Gender = false and also having All grand children Gender = false).

LINQ - filter collection inside collection

4 Answers4

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