Question

I’ve been scouring multiple resources and can’t figure this one out; I am trying to filter an Array of objects based on a Property that is nested a couple levels deep. I’ve simplified things, so let’s say I have the following classes:

class A {
  B[] bb;
}

class B 
  C[] cc;
}

class C {
  string value;
}

And now the code:

A[] aa = ...;
A[] filteredAa = aa.Where(... //NEED HELP HERE

What I want to do is filter the aa array such that it gives me only those A elements that have at least one B element that have at least one C element has a value of “hello” (e.g. aa[0] would be included in the filteredAa array if aa[0].bb[3].cc[2].value = “hello”).

Can this type of filtering even be done? I think and hope this makes sense, but please let me know if I can clarify any further.

Answer 1

You need to use Any – and it sounds like you need to use it twice:

var query = aa.Where(a => a.bb.Any(b => b.cc.Any(c => c.value == "hello")));

So working up from the inside:

• A C object is useful if its value is “hello”
• A B object is useful if any of its C values are useful
• An A object is useful if any of its B values are useful
• Where filters a sequence of A objects, leaving only the useful ones

You can use ToArray() at the end if you really want an array, but I would typically use ToList or just keep it as an IEnumerable<A>.