code: public Histogram modifyEventCounters(BiFunction<Range, Double, Double> fn) {
          return new Histogram(stream()
                  .map(entry -> {
                      entry.setCount(fn.apply(entry.getRange(), entry.getCount()));
                      return entry;
                  }));
      }
docs: Create a new histogram, after applying the function on each of the event
  counters.