Chunk example

bookshelf.rb

Book = Struct.new(:title, :year_published) do
  def decade_published
	year_published - year_published % 10
  end
  def to_s
	"#{title} (#{year_published})"
  end
end

bookshelf = [
  Book.new("The Great Gatsby", 1925),
  Book.new("Gone with the Wind", 1936),
  Book.new("The Hobbit", 1937),
  Book.new("The Little Prince", 1940),
  Book.new("1984", 1949),
  Book.new("The Catcher in the Rye", 1951),
  Book.new("To Kill a Mockingbird", 1960),
]

books_by_decade = bookshelf.chunk { |book| "#{book.decade_published}'s" }
puts books_by_decade.to_a
# 1920's
# The Great Gatsby (1925)
# 1930's
# Gone with the Wind (1936)
# The Hobbit (1937)
# 1940's
# The Little Prince (1940)
# 1984 (1949)
# 1950's
# The Catcher in the Rye (1951)
# 1960's
# To Kill a Mockingbird (1960)