Nested hash for nested group by

00_task.rb

def base_for_nested_group_by(x)
end

# f(0)
Hash.new # or ArgumentError

# f(1)
Hash.new {|h1, k1| h1[k1] = []}

# f(2)
Hash.new{|h1,k1| h1[k1] = Hash.new{|h2,k2| h2[k2] = []}}

# f(3)
Hash.new{|h1,k1| h1[k1] = Hash.new{|h2,k2| h2[k2] = Hash.new{|h3,k3| h3[k3] = []}}}

# ...

10_solution_one.rb

def base_for_nested_group_by(n)
  def nested_hash_source_code(n)
    raise ArgumentError.new('Give a positive integer') if n < 1
    return "Hash.new {|h#{n},k#{n}|h#{n}[k#{n}] = [] }" if n == 1
    "Hash.new {|h#{n},k#{n}| h#{n}[k#{n}] = #{nested_hash_source_code(n-1)} }"
  end

  eval nested_hash_source_code(n.to_i)
end

20_ok_no_eval.rb

def base_for_nested_group_by(n)
  raise ArgumentError.new('Give a positive integer') if n < 1
  return Hash.new { |h, k| h[k] = [] } if n == 1
  Hash.new {|h, k| h[k] = base_for_nested_group_by(n-1) }
end