public void PrepareData()
        {
            // full dataset https://github.com/le-scientifique/torchDatasets/raw/master/dbpedia_csv.tar.gz
            var url = "https://raw.githubusercontent.com/SciSharp/TensorFlow.NET/master/data/dbpedia_subset.zip";

            Web.Download(url, dataDir, "dbpedia_subset.zip");
            Compress.UnZip(Path.Combine(dataDir, "dbpedia_subset.zip"), Path.Combine(dataDir, "dbpedia_csv"));

            Console.WriteLine("Building dataset...");
            var(x, y) = (new int[0][], new int[0]);

            if (ModelName == "char_cnn")
            {
                (x, y, alphabet_size) = DataHelpers.build_char_dataset(TRAIN_PATH, "char_cnn", CHAR_MAX_LEN);
            }
            else
            {
                var word_dict = DataHelpers.build_word_dict(TRAIN_PATH);
                vocabulary_size = len(word_dict);
                (x, y)          = DataHelpers.build_word_dataset(TRAIN_PATH, word_dict, WORD_MAX_LEN);
            }

            Console.WriteLine("\tDONE ");

            var(train_x, valid_x, train_y, valid_y) = train_test_split(x, y, test_size: 0.15f);
            Console.WriteLine("Training set size: " + train_x.shape[0]);
            Console.WriteLine("Test set size: " + valid_x.shape[0]);
        }
        protected virtual bool RunWithBuiltGraph(Session session, Graph graph)
        {
            Console.WriteLine("Building dataset...");
            var(x, y, alphabet_size) = DataHelpers.build_char_dataset("train", model_name, CHAR_MAX_LEN, DataLimit);

            var(train_x, valid_x, train_y, valid_y) = train_test_split(x, y, test_size: 0.15f);

            ITextClassificationModel model = null;

            switch (model_name) // word_cnn | char_cnn | vd_cnn | word_rnn | att_rnn | rcnn
            {
            case "word_cnn":
            case "char_cnn":
            case "word_rnn":
            case "att_rnn":
            case "rcnn":
                throw new NotImplementedException();
                break;

            case "vd_cnn":
                model = new VdCnn(alphabet_size, CHAR_MAX_LEN, NUM_CLASS);
                break;
            }
            // todo train the model
            return(false);
        }
        protected virtual bool RunWithImportedGraph(Session sess, Graph graph)
        {
            var stopwatch = Stopwatch.StartNew();

            Console.WriteLine("Building dataset...");
            var path = UseSubset ? SUBSET_PATH : TRAIN_PATH;

            int[][] x               = null;
            int[]   y               = null;
            int     alphabet_size   = 0;
            int     vocabulary_size = 0;

            if (model_name == "vd_cnn")
            {
                (x, y, alphabet_size) = DataHelpers.build_char_dataset(path, model_name, CHAR_MAX_LEN, DataLimit = null, shuffle: !UseSubset);
            }
            else
            {
                var word_dict = DataHelpers.build_word_dict(TRAIN_PATH);
                vocabulary_size = len(word_dict);
                (x, y)          = DataHelpers.build_word_dataset(TRAIN_PATH, word_dict, WORD_MAX_LEN);
            }

            Console.WriteLine("\tDONE ");

            var(train_x, valid_x, train_y, valid_y) = train_test_split(x, y, test_size: 0.15f);
            Console.WriteLine("Training set size: " + train_x.len);
            Console.WriteLine("Test set size: " + valid_x.len);

            Console.WriteLine("Import graph...");
            var meta_file = model_name + ".meta";

            tf.train.import_meta_graph(Path.Join("graph", meta_file));
            Console.WriteLine("\tDONE " + stopwatch.Elapsed);

            sess.run(tf.global_variables_initializer());
            var saver = tf.train.Saver(tf.global_variables());

            var    train_batches         = batch_iter(train_x, train_y, BATCH_SIZE, NUM_EPOCHS);
            var    num_batches_per_epoch = (len(train_x) - 1) / BATCH_SIZE + 1;
            double max_accuracy          = 0;

            Tensor    is_training = graph.OperationByName("is_training");
            Tensor    model_x     = graph.OperationByName("x");
            Tensor    model_y     = graph.OperationByName("y");
            Tensor    loss        = graph.OperationByName("loss/Mean"); // word_cnn
            Operation optimizer   = graph.OperationByName("loss/Adam"); // word_cnn
            Tensor    global_step = graph.OperationByName("Variable");
            Tensor    accuracy    = graph.OperationByName("accuracy/accuracy");

            stopwatch = Stopwatch.StartNew();
            int i = 0;

            foreach (var(x_batch, y_batch, total) in train_batches)
            {
                i++;
                var train_feed_dict = new FeedDict
                {
                    [model_x]     = x_batch,
                    [model_y]     = y_batch,
                    [is_training] = true,
                };
                //Console.WriteLine("x: " + x_batch.ToString() + "\n");
                //Console.WriteLine("y: " + y_batch.ToString());
                // original python:
                //_, step, loss = sess.run([model.optimizer, model.global_step, model.loss], feed_dict = train_feed_dict)
                var result = sess.run(new ITensorOrOperation[] { optimizer, global_step, loss }, train_feed_dict);
                loss_value = result[2];
                var step = (int)result[1];
                if (step % 10 == 0)
                {
                    var estimate = TimeSpan.FromSeconds((stopwatch.Elapsed.TotalSeconds / i) * total);
                    Console.WriteLine($"Training on batch {i}/{total} loss: {loss_value}. Estimated training time: {estimate}");
                }

                if (step % 100 == 0)
                {
                    // # Test accuracy with validation data for each epoch.
                    var valid_batches = batch_iter(valid_x, valid_y, BATCH_SIZE, 1);
                    var(sum_accuracy, cnt) = (0.0f, 0);
                    foreach (var(valid_x_batch, valid_y_batch, total_validation_batches) in valid_batches)
                    {
                        var valid_feed_dict = new FeedDict
                        {
                            [model_x]     = valid_x_batch,
                            [model_y]     = valid_y_batch,
                            [is_training] = false
                        };
                        var   result1        = sess.run(accuracy, valid_feed_dict);
                        float accuracy_value = result1;
                        sum_accuracy += accuracy_value;
                        cnt          += 1;
                    }

                    var valid_accuracy = sum_accuracy / cnt;

                    print($"\nValidation Accuracy = {valid_accuracy}\n");

                    //    # Save model
                    if (valid_accuracy > max_accuracy)
                    {
                        max_accuracy = valid_accuracy;
                        // saver.save(sess, $"{dataDir}/{model_name}.ckpt", global_step: step.ToString());
                        print("Model is saved.\n");
                    }
                }
            }

            return(false);
        }