code: func (s Sample) IQR() float64 {
  	if !s.Sorted {
  		s = *s.Copy().Sort()
  	}
  	return s.Quantile(0.75) - s.Quantile(0.25)
  }
docs: // IQR returns the interquartile range of the Sample.
  //
  // This is constant time if s.Sorted and s.Weights == nil.