Filtering a Backbone Collection returns an array of Models

Sample Code:

this.books = this.getBooksFromDatabase();
this.publishedBooks = this.books.filter(function(book) {
  return book.get("isPublished") === "1";
});

Here lies the problem:

this.books.filter, returns an array of the models. I've tried wrapping the array, as such:

var publishedBooks = _( this.books.filter(function(book) {
  return book.get("isPublished") === "1";
}))

as recommended by this post: https://github.com/documentcloud/backbone/issues/120

But i still can't run things like: publishedBooks.each(...), or publishedBooks.get(...)

What am I missing? Is there a way to convert the returned array into a collection?