Book Index Sort

book_index_sort.rb

# Sorts an array of decimals as if the were the chapters and sections of a book
sections = [3.1, 3.11, 3.2, 3.3, 3.8, 3.7 , 3.8, 3.9, 3.10]

sections.sort do |e1, e2|
  if e1.to_i == e2.to_i # Comparing sections within the same chapter
    # Get the real value for the section within the chapter
    n1 = e1 + e1.to_s.split('.')[1].to_i
    n2 = e2 + e2.to_s.split('.')[1].to_i
    # Compare using the real value of the section
    n1 <=> n2
  else # Comparing different chapters
    e1 <=> e2
  end
end
# => [3.1, 3.1, 3.2, 3.3, 3.7, 3.8, 3.8, 3.9, 3.11]

# As you can see, 3.10 is represented as if it was 3.1, so it may be better
# to store the sections as strings.