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c#lambdaiequalitycomparer
Florian
Florian

Reputation: 4728

Specify equality with a lambda expression

I want to compare 2 collections. One of these is a List<string> and the other is a List<Book>. Book has a Isbn property of type string, and I want write something like that : 

List<string> isbnBooks= new List<string> {"978-1933988276", "978-0321146533", "3"};
List<Book> books = new List<Book>();

books.Add(new Book { Isbn="978-1933988276", Name="The Art of Unit Testing"});
books.Add(new Book { Isbn="978-0321146533", Name="TDD By Example"});
books.Add(new Book { Isbn="978-0321503626", Name="Growing Object-Oriented Software"});

// What I want to write
var intersectedBooks = books.Intersect(books, isbnBooks, (book, isbn) => book.Isbn == isbn));

I would like specify equality in the method. Is it possible ? Or should I mandatory create a BookComparer which implements IEqualityComparer interface ?

Regards,

Florian

Upvotes: 0

Views: 989

Answers (2)

Thom Smith
Thom Smith

Reputation: 14086

Or, you could always do:

var intersectedBooks = books.Select(book=>book.Isbn).Intersect(isbnBooks);

Upvotes: 2

Jon Skeet
Jon Skeet

Reputation: 1501656

Intersect simply doesn't work with different collection types. In this case it looks like it would be simpler to write:

HashSet<string> isbns = new HashSet<string> isbnBooks();   
var intersectedBooks = books.Where(book => isbns.Contains(book.Isbn));

Or you could just do a join, of course:

var knownBooks = from book in books
                 join isbn in isbnBooks on book.Isbn equals isbn
                 select book;

(The two approaches are broadly equivalent.)

Upvotes: 3

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