code: func (d *Document) WordDensity() map[string]float64 {
  	density := make(map[string]float64)
  	for word, freq := range d.WordFrequency {
  		val, _ := stats.Round(float64(freq)/d.NumWords, 3)
  		density[word] = val
  	}
  	return density
  }
docs: // WordDensity returns a map of each word and its density.