Fixed Value Error when doing HDFStore.Select of contiguous mixed-data (pandas-dev#17670)

Author: amolkahat

doc/source/whatsnew/v0.21.0.txt

@@ -603,6 +603,7 @@ I/O
 - Bug in :func:`read_html` where import check fails when run in multiple threads (:issue:`16928`)
 - Bug in :func:`read_csv` where automatic delimiter detection caused a ``TypeError`` to be thrown when a bad line was encountered rather than the correct error message (:issue:`13374`)
 - Bug in ``DataFrame.to_html()`` with ``notebook=True`` where DataFrames with named indices or non-MultiIndex indices had undesired horizontal or vertical alignment for column or row labels, respectively (:issue:`16792`)
+- Bug in :func:`HDFStore.select` when reading a contiguous mixed-data table featuring VLArray (:issue:`17021`)
 
 Plotting
 ^^^^^^^^

pandas/io/pytables.py

@@ -2441,13 +2441,12 @@ def read_array(self, key, start=None, stop=None):
         """ read an array for the specified node (off of group """
         import tables
         node = getattr(self.group, key)
-        data = node[start:stop]
         attrs = node._v_attrs
 
         transposed = getattr(attrs, 'transposed', False)
 
         if isinstance(node, tables.VLArray):
-            ret = data[0]
+            ret = node[0][start:stop]
         else:
             dtype = getattr(attrs, 'value_type', None)
             shape = getattr(attrs, 'shape', None)
@@ -2456,7 +2455,7 @@ def read_array(self, key, start=None, stop=None):
                 # length 0 axis
                 ret = np.empty(shape, dtype=dtype)
             else:
-                ret = data
+                ret = node[start:stop]
 
             if dtype == u('datetime64'):
 

pandas/tests/io/test_pytables.py

@@ -4391,6 +4391,19 @@ def test_path_pathlib(self):
             lambda p: pd.read_hdf(p, 'df'))
         tm.assert_frame_equal(df, result)
 
+    @pytest.mark.parametrize('start, stop', [(0, 2), (1, 2), (None, None)])
+    def test_contiguous_mixed_data_table(self, start, stop):
+        # GH 17021
+        # ValueError when reading a contiguous mixed-data table ft. VLArray
+        df = DataFrame({'a': Series([20111010, 20111011, 20111012]),
+                        'b': Series(['ab', 'cd', 'ab'])})
+
+        with ensure_clean_store(self.path) as store:
+            store.append('test_dataset', df)
+
+            result = store.select('test_dataset', start=start, stop=stop)
+            assert_frame_equal(df[start:stop], result)
+
     def test_path_pathlib_hdfstore(self):
         df = tm.makeDataFrame()