thiago2.rb

dirs = [
  "a1",
  "a2",
  "a3",
  "b1",
  "b2",
  # missing b3
  "b4",
  "b5",
  # missing all c
  "d1",
  "d2",
  # missing all e
  "f1",
  "f2",
  "f3",
  # missing f4
  "f5",
  "f6",
]

groups = [
  [
    "a1",
    "a2",
    "a3"
  ],
  [
    "b1",
    "b2",
    "b3",
    "b4",
    "b5"
  ],
  [
    "c1",
    "c2"
  ],
  [
    "d1",
    "d2"
  ],
  [
    "e1",
    "e2"
  ],
  [
    "f1",
    "f2",
    "f3",
    "f4",
    "f5",
    "f6"
  ]
]

index_table = {}
index = 1
sub_index = 0

groups.each do |group|
  group.each do |dir|
    if dirs.include?(dir)
      sub_index += 1
      index_table["#{index}.#{sub_index}"] = dir
    end
  end

  # At least one dir in the group exists, increment index
  if sub_index > 0
    index += 1
  end

  # Reset sub_index
  sub_index = 0
end

pp index_table