code: public static <C extends Compound> Map<C, Double> getDistribution(Sequence<C> sequence) {
  		Map<C, Double> results = new HashMap<C, Double>();
  		Map<C, Integer> composition = getComposition(sequence);
  		double length = sequence.getLength();
  		for (Map.Entry<C, Integer> entry : composition.entrySet()) {
  			double dist = entry.getValue().doubleValue() / length;
  			results.put(entry.getKey(), dist);
  		}
  		return results;
  	}
docs: Analogous to {@link #getComposition(Sequence)} but returns the
  distribution of that {@link Compound} over the given sequence.
  
  @param <C> The type of compound to look for
  @param sequence The type of sequence to look over
  @return Returns the decimal fraction of the compounds in the given
  sequence. Any compound not in the Map will return a fraction of 0.