How to flatten nested objects with linq expression

Question

I am trying to flatten nested objects like this:

public class Book
{
    public string Name { get; set; }
    public IList<Chapter> Chapters { get; set; }
}

public class Chapter
{
    public string Name { get; set; }
    public IList<Page> Pages { get; set; }
}


public class Page
{
    public string Name { get; set; }
}

Let me make an example. This is the data I have

Book: Pro Linq 
{ 
   Chapter 1: Hello Linq 
   {
      Page 1, 
      Page 2, 
      Page 3
   },
   Chapter 2: C# Language enhancements
   {
      Page 4
   },
}

The result I am looking for is the following flat list:

"Pro Linq", "Hello Linq", "Page 1"
"Pro Linq", "Hello Linq", "Page 2"
"Pro Linq", "Hello Linq", "Page 3"
"Pro Linq", "C# Language enhancements", "Page 4"

How could I accomplish this? I could do it with a select new but I've been told that a SelectMany would be enough.

Yuriy Faktorovich · Accepted Answer · 2011-06-21 16:49:15Z

248

myBooks.SelectMany(b => b.Chapters
    .SelectMany(c => c.Pages
        .Select(p => b.Name + ", " + c.Name + ", " + p.Name)));

answered Jun 21, 2011 at 16:49

Yuriy Faktorovich

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13 Comments

ab_732 Over a year ago

Awesome!!! What if I would have a result a new object, like FlatBook{BookName, ChapterName, PageName} ?

user7116 Over a year ago

@abx78: simply alter the last select: .Select(p => new FlatBook(b.Name, c.Name, p.Name))

Homer Over a year ago

does this produce the same result? myBooks.SelectMany(b => b.Chapters).SelectMany(c => c.Pages).Select(p => b.Name + ", " + c.Name + ", " + p.Name);

The Muffin Man Over a year ago

So how would you rewrite this to support an N number of nested objects?

Yuriy Faktorovich Over a year ago

@Mastro how about

myBooks.SelectMany(b => b.Chapters == null || !b.Chapters.Any()? new []{b.Name + " has no Chapters"} : b.SelectMany(c => c.Pages.Select(p => b.Name + ", " + c.Name + ", " + p.Name)));

|

shA.t · Accepted Answer · 2016-02-23 13:43:24Z

57

Assuming books is a List of Book:

var r = from b in books
    from c in b.Chapters
    from p in c.Pages
    select new {BookName = b.Name, ChapterName = c.Name, PageName = p.Name};

edited Feb 23, 2016 at 13:43

shA.t

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answered Jun 21, 2011 at 16:58

boca

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1 Comment

user7116 Over a year ago

+1, even though any IEnumerable<Book> will do, doesn't need a List<Book>.

Madhukar Bhandari · Accepted Answer · 2015-02-02 09:41:08Z

7

myBooks.SelectMany(b => b.Chapters
    .SelectMany(c => c.Pages
        .Select(p => new 
                {
                    BookName = b.Name ,
                    ChapterName = c.Name , 
                    PageName = p.Name
                });

answered Feb 2, 2015 at 9:41

Madhukar Bhandari

991 silver badge8 bronze badges

1 Comment

oɔɯǝɹ Over a year ago

While this code sample may answer the question, it lacks explanation. As it stands now, it adds no value, and stands the change of being downvoted / deleted. Please add some explanation what is does and why it is a solution for the problem of the OP.

Mastro · Accepted Answer · 2014-06-25 00:54:08Z

I was trying to do this as well, and from Yuriy's comments and messing with linqPad I have this..

Note that I don't have books, chapters, pages, I have person (books), companyPerson (chapters) and companies (pages)

from person in Person
                           join companyPerson in CompanyPerson on person.Id equals companyPerson.PersonId into companyPersonGroups
                           from companyPerson in companyPersonGroups.DefaultIfEmpty()
                           select new
                           {
                               ContactPerson = person,
                               ContactCompany = companyPerson.Company
                           };

or

Person
   .GroupJoin (
      CompanyPerson, 
      person => person.Id, 
      companyPerson => companyPerson.PersonId, 
      (person, companyPersonGroups) => 
         new  
         {
            person = person, 
            companyPersonGroups = companyPersonGroups
         }
   )
   .SelectMany (
      temp0 => temp0.companyPersonGroups.DefaultIfEmpty (), 
      (temp0, companyPerson) => 
         new  
         {
            ContactPerson = temp0.person, 
            ContactCompany = companyPerson.Company
         }
   )

Ref site I used: http://odetocode.com/blogs/scott/archive/2008/03/25/inner-outer-lets-all-join-together-with-linq.aspx

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