gistfile1.rb

require 'active_support/core_ext/array'

items = ["African", "Ambient", "Asian", "Avant-garde", "Blues", "Breakbeat", "Caribbean", "Comedy", "Country", "Disco", "Downtempo", "Drum & Bass", "Easy listening", "Electro", "Electronic", "Folk", "Hardcore", "Hardstyle", "Hip hop", "House", "Industrial", "Jazz", "Jungle", "Latin", "Pop", "R&B", "Rock", "Soul", "Techno", "Trance"]

letters = ('a'..'z')
puts letters.to_a.map(&:upcase).join(' ')

last_letter = '`' # ` is the char before 'a'
items.in_groups_of(2).each do |group|
  next_letter = group.compact.map { |item| item[0].downcase }.last
  if next_letter != last_letter
    (last_letter.succ..next_letter).each do |letter|
      puts %{<a name="#{letter}">}
    end
  end
  last_letter = next_letter

  puts group.inspect
end