Fix TSDataSampler Slicing Bug #1716 (#1803)

* Fix TSDataSampler Slicing Bug #1716

* Fix TSDataSampler Slicing Bug #1716

* Fix TSDataSampler Slicing Bug #1716

* Fix TSDataSampler Slicing Bug with simplyer implmentation#1716
 with Simplified Implementation

* Refactor: Fix CI errors by addressing pylint formatting issues

* Refactor: Remove extraneous whitespace for improved code formatting with Black

qlib/data/dataset/__init__.py

@@ -403,7 +403,7 @@ def __init__(
             np.full((1, self.data_arr.shape[1]), np.nan, dtype=self.data_arr.dtype),
             axis=0,
         )
-        self.nan_idx = -1  # The last line is all NaN
+        self.nan_idx = len(self.data_arr) - 1  # The last line is all NaN; setting it to -1 can cause bug #1716
 
         # the data type will be changed
         # The index of usable data is between start_idx and end_idx

tests/data_mid_layer_tests/test_dataset.py

@@ -5,8 +5,9 @@
 import pytest
 import sys
 from qlib.tests import TestAutoData
-from qlib.data.dataset import TSDatasetH
+from qlib.data.dataset import TSDatasetH, TSDataSampler
 import numpy as np
+import pandas as pd
 import time
 from qlib.data.dataset.handler import DataHandlerLP
 
@@ -98,6 +99,54 @@ def testTSDataset(self):
             print(idx[i])
 
 
+class TestTSDataSampler(unittest.TestCase):
+    def test_TSDataSampler(self):
+        """
+        Test TSDataSampler for issue #1716
+        """
+        datetime_list = ["2000-01-31", "2000-02-29", "2000-03-31", "2000-04-30", "2000-05-31"]
+        instruments = ["000001", "000002", "000003", "000004", "000005"]
+        index = pd.MultiIndex.from_product(
+            [pd.to_datetime(datetime_list), instruments], names=["datetime", "instrument"]
+        )
+        data = np.random.randn(len(datetime_list) * len(instruments))
+        test_df = pd.DataFrame(data=data, index=index, columns=["factor"])
+        dataset = TSDataSampler(test_df, datetime_list[0], datetime_list[-1], step_len=2)
+        print()
+        print("--------------dataset[0]--------------")
+        print(dataset[0])
+        print("--------------dataset[1]--------------")
+        print(dataset[1])
+        assert len(dataset[0]) == 2
+        self.assertTrue(np.isnan(dataset[0][0]))
+        self.assertEqual(dataset[0][1], dataset[1][0])
+        self.assertEqual(dataset[1][1], dataset[2][0])
+        self.assertEqual(dataset[2][1], dataset[3][0])
+
+    def test_TSDataSampler2(self):
+        """
+        Extra test TSDataSampler to prevent incorrect filling of nan for the values at the front
+        """
+        datetime_list = ["2000-01-31", "2000-02-29", "2000-03-31", "2000-04-30", "2000-05-31"]
+        instruments = ["000001", "000002", "000003", "000004", "000005"]
+        index = pd.MultiIndex.from_product(
+            [pd.to_datetime(datetime_list), instruments], names=["datetime", "instrument"]
+        )
+        data = np.random.randn(len(datetime_list) * len(instruments))
+        test_df = pd.DataFrame(data=data, index=index, columns=["factor"])
+        dataset = TSDataSampler(test_df, datetime_list[2], datetime_list[-1], step_len=3)
+        print()
+        print("--------------dataset[0]--------------")
+        print(dataset[0])
+        print("--------------dataset[1]--------------")
+        print(dataset[1])
+        for i in range(3):
+            self.assertFalse(np.isnan(dataset[0][i]))
+            self.assertFalse(np.isnan(dataset[1][i]))
+        self.assertEqual(dataset[0][1], dataset[1][0])
+        self.assertEqual(dataset[0][2], dataset[1][1])
+
+
 if __name__ == "__main__":
     unittest.main(verbosity=10)