Find all combinations of characters in given string

string_combinations.rb

def combinations(s)
  return [s] if s.length == 1

  chars = s.chars.to_a

  chars.each_with_object([]) do |ch, cs|
    rest = chars.drop(chars.find_index(ch) + 1).join
    cs << ch
    combinations(rest).each do |comb|
      cs << (ch + comb)
    end
  end
end


p combinations('wxyz')
# >> ["w", "wx", "wxy", "wxyz", "wxz", "wy", "wyz", "wz", "x", "xy", "xyz", "xz", "y", "yz", "z"]