code: public SufficientStatistics getStatisticByName(String name) {
      if (names.contains(name)) {
        return statistics.get(names.getIndex(name));
      }
      return null;
    }
docs: Gets a particular set of sufficient statistics from this vector.
  The returned statistics are a reference to statistics in {@code this},
  and therefore may be mutated to affect the value of {@code this}.
  Returns {@code null} if no statistics exist with {@code name}.
  
  @return