How to remove all instances inside a list where a contained list does not contain all values given? help please

So I am trying to set up a searching system, for which I need to go through each ‘book’ in a list and remove each one that does not match the given ‘genres’. each book contains a list of genre ID’s.

I used this and I am sure it used to work but maybe it was my imagination…

books.RemoveAll(i => i.genres != null && !genres.All(x => i.genres.Any(y => x == y)));

does anyone know how to implament this feature?

Thank you!

Answers:

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Method 1

It sounds like you’re saying that a book has many genres, and you want to filter a list of books based on a list of genres such that all books in the list have all their genres in the genre list.

This answer is also assuming that the Genre class implements IComparable<Genre>. In this example genres is a List<string>:

public class Book
{
    public string Title;
    public List<string> Genres;
}

Then for sample data, we can create a list of books and a list of genres:

var genres = new List<string> {"Horror", "Action", "Adventure"};

var books = new List<Book>
{
    new Book {Title = "The Shining", Genres = new List<string> {"Horror", "Adventure"}},
    new Book {Title = "Sahara", Genres = new List<string> {"Action", "Adventure"}},
    new Book {Title = "The Odds", Genres = new List<string> {"Action", "Comedy"}}
};

If that’s the case, this should do the trick:

books.RemoveAll(book =>
    book.Genres != null &&
    book.Genres.Any(genre => !genres.Contains(genre)));

// The last book is removed from the list, because 'genres' doesn't contain "Comedy"

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