Using LINQ, select list of objects inside another list of objects

Question

public class ClassA
{
     public string MyString {get; set;}
}

public class ClassB
{
     public List<ClassA> MyObjects {get; set;}
}

List<ClassB> classBList = new List<ClassB>();
var results = (from i in classBList select i.MyObjects).Distinct();

I want a distinct list of all the ClassA objects in the classBList. How do I go about this using LINQ? I'm thinking about a nested query, but couldn't quite figure it out. Any help is very appreciated.

SLaks · Accepted Answer · 2010-10-14 15:02:23Z

118

You're trying to select multiple result objects for each ClassB object in the original list.

Therefore, you're looking for the SelectMany extension method:

var results = classBList.SelectMany(b => b.MyObjects).Distinct();

If you want to use query expressions, you'll need to use two from clauses:

var results = (from b in classBList from a in b.MyObjects select a).Distinct();

answered Oct 14, 2010 at 15:02

SLaks

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2 Comments

Justin Niessner Over a year ago

Does the query syntax you provide use SelectMany once translated? I'm a tad naive when it comes to query syntax since it always looks more verbose (except in join situations).

SLaks Over a year ago

@Justin: Yes; those two expressions should compile identically.

Justin Niessner · Accepted Answer · 2010-10-14 15:02:31Z

19

You want to use IEnumerable.SelectMany() Extension Method to flatten the hierarchy:

var result = classBList.SelectMany(b => b.MyObjects).Distinct();

answered Oct 14, 2010 at 15:02

Justin Niessner

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