# File narray_ext.rb, line 186
  def median(rank=nil)
    shape = self.shape
    rank = shape.size-1 if rank==nil
    s = sort(rank).reshape!(true,*shape[rank+1..-1])
    n = s.shape[0]
    if n%2==1
      s[n/2,false]
    else
      s[n/2-1..n/2,false].sum(0)/2
    end
  end