add pad preprocessing for `imdb` dataset

src/TensorFlowNET.Keras/Datasets/Imdb.cs

@@ -40,6 +40,8 @@ namespace Tensorflow.Keras.Datasets
             int oov_char= 2,
             int index_from = 3)
         {
+            if (maxlen == -1) throw new InvalidArgumentError("maxlen must be assigned.");
+            
             var dst = Download();
 
             var lines = File.ReadAllLines(Path.Combine(dst, "imdb_train.txt"));
@@ -51,7 +53,7 @@ namespace Tensorflow.Keras.Datasets
                 x_train_string[i] = lines[i].Substring(2);
             }
 
-            var x_train = np.array(x_train_string);
+            var x_train = keras.preprocessing.sequence.pad_sequences(PraseData(x_train_string), maxlen: maxlen);
 
             File.ReadAllLines(Path.Combine(dst, "imdb_test.txt"));
             var x_test_string = new string[lines.Length];
@@ -62,7 +64,7 @@ namespace Tensorflow.Keras.Datasets
                 x_test_string[i] = lines[i].Substring(2);
             }
 
-            var x_test = np.array(x_test_string);
+            var x_test = keras.preprocessing.sequence.pad_sequences(PraseData(x_test_string), maxlen: maxlen);
 
             return new DatasetPass
             {
@@ -93,5 +95,23 @@ namespace Tensorflow.Keras.Datasets
             return dst;
             // return Path.Combine(dst, file_name);
         }
+
+        protected IEnumerable<int[]> PraseData(string[] x)
+        {
+            var data_list = new List<int[]>();
+            for (int i = 0; i < len(x); i++)
+            {
+                var list_string = x[i];
+                var cleaned_list_string = list_string.Replace("[", "").Replace("]", "").Replace(" ", "");
+                string[] number_strings = cleaned_list_string.Split(',');
+                int[] numbers = new int[number_strings.Length];
+                for (int j = 0; j < number_strings.Length; j++)
+                {
+                    numbers[j] = int.Parse(number_strings[j]);
+                }
+                data_list.Add(numbers);
+            }
+            return data_list;
+        }
     }
 }