pascal's triangle in ruby

gistfile1.rb

def pascalsTriangle(n)
  (1..n).inject([]) do |final, level|
    final << (1..level).inject([]) do |horizontal, index|
      if index == 1 || index == level
        horizontal << 1
      else
        horizontal << (final[level - 2][index - 2]) + (final[level - 2][index - 1])
      end
    end
    final
  end
end