public static void AddRange <TKey, TBin>(
     this IHistogram <TKey, TBin> hist,
     IEnumerable <KeyValuePair <TKey, TBin> > keysAndIncrements)
     where TBin : struct
 {
     foreach (var kvp in keysAndIncrements)
     {
         hist.Add(kvp);
     }
 }
 public static void AddRange <TKey, TBin>(
     this IHistogram <TKey, TBin> hist,
     IEnumerable <TKey> keys,
     TBin increment)
     where TBin : struct
 {
     foreach (var key in keys)
     {
         hist.Add(key, increment);
     }
 }