public static IEnumerable <UniqueNGramCollection> Create(IEnumerable <NGramCollection> ngrams)
        {
            List <UniqueNGramCollection> uniqueNgramCollections = new List <UniqueNGramCollection>();

            if (ngrams != null)
            {
                foreach (NGramCollection gram in ngrams)
                {
                    UniqueNGramCollection uniqueCollection = UniqueNGramCollection.Create(gram);
                    uniqueNgramCollections.Add(uniqueCollection);
                }
            }

            return(uniqueNgramCollections);
        }
        public static UniqueNGramCollection Create(NGramCollection ngrams)
        {
            if (ngrams == null)
            {
                throw new ArgumentNullException(nameof(ngrams));
            }

            UniqueNGramCollection uniqueNgrams = new UniqueNGramCollection(ngrams.GramLength);

            foreach (NGram gram in ngrams.Grams)
            {
                uniqueNgrams.Add(gram);
            }

            return(uniqueNgrams);
        }