public BookData getByPubYear(int year){
		BookData subset = new BookData();
		
		//Check each book in books
		for(int i=0; i<books.size(); i++){
			int temp = books.get(i).getPubYear();
			//If the pub. year matches, add it to subset
			if(temp == year){
				subset.addBook(books.get(i));
			}
		}
		//return any matching books
		return subset;
	}