gistfile1.rb

def quartile(array, q=3)
  return array.first if array.length <= 1
  sorted = array.sort
  return sorted.last if q == 4
  quartile_position = 0.25 * (q*sorted.length + 4 - q)
  quartile_int = quartile_position.to_i
  lower = sorted[quartile_int - 1]
  upper = sorted[quartile_int]
  lower + (upper - lower) * (quartile_position - quartile_int)
end