public E argMax() {
    double maxCount = Double.NEGATIVE_INFINITY;
    E maxKey = null;
    for (Map.Entry<E, Double> entry : entries.entrySet()) {
      if (entry.getValue() > maxCount || maxKey == null) {
        maxKey = entry.getKey();
        maxCount = entry.getValue();
      }
    }
    return maxKey;
  }