Fix: VariableLengthArray failed for zero length

Signed-off-by: Matthias Kümmerer <[email protected]>

pysaliency/utils/__init__.py

@@ -28,7 +28,7 @@ def build_padded_2d_array(arrays, max_length=None, padding_value=np.nan):
         max_length = np.max([len(a) for a in arrays])
 
     #output = np.ones((len(arrays), max_length), dtype=np.asarray(arrays[0]).dtype)
-    dtype = np.asarray(arrays[0]).dtype
+    dtype = np.asarray(arrays[0]).dtype if arrays else np.float64
 
     if np.issubdtype(dtype, np.integer) and padding_value is np.nan:
         dtype = np.float64

pysaliency/utils/variable_length_array.py

@@ -52,7 +52,7 @@ def __init__(self, data: Union[np.ndarray, List[list]], lengths: Optional[np.nda
             else:
                 if not data.ndim >= 2:
                     raise ValueError("If data is a numpy array, it has to be at least 2-dimensional")
-                if np.max(lengths) > data.shape[1]:
+                if lengths and np.max(lengths) > data.shape[1]:
                     raise ValueError("The specified lengths are larger than the number of columns in the data array")
 
         else:
@@ -63,7 +63,7 @@ def __init__(self, data: Union[np.ndarray, List[list]], lengths: Optional[np.nda
         if isinstance(data, np.ndarray):
             self._data = data
         else:
-            self._data = build_padded_2d_array(data, max_length=np.max(lengths))
+            self._data = build_padded_2d_array(data, max_length=np.max(lengths) if lengths else 0)
 
         # max_len = np.max(lengths)
         # self._data = np.full((len(data), max_len), np.nan)
@@ -96,11 +96,11 @@ def __getitem__(self, index):
             # new_data = self._data[index, :max_length]
             # return VariableLengthArray(new_data, new_lengths)
 
-    def copy(self):
+    def copy(self) -> 'VariableLengthArray':
         return VariableLengthArray(self._data.copy(), self.lengths.copy())
 
 
-def concatenate_variable_length_arrays(arrays: List[VariableLengthArray]):
+def concatenate_variable_length_arrays(arrays: List[VariableLengthArray]) -> VariableLengthArray:
     """
     Concatenate a list of VariableLengthArray objects along the first axis.
 

tests/utils/test_variable_length_array.py

@@ -174,4 +174,26 @@ def test_variable_length_array_concatenate():
     expected = VariableLengthArray(concatenated_data)
 
     np.testing.assert_array_equal(concatenated_array._data, expected._data)
-    np.testing.assert_array_equal(concatenated_array.lengths, expected.lengths)
+    np.testing.assert_array_equal(concatenated_array.lengths, expected.lengths)
+
+
+def test_variable_length_array_zero_length_from_2d_array():
+    data = np.empty((0, 0))
+    lengths = np.array([])
+    array = VariableLengthArray(data, lengths)
+
+    assert len(array) == 0
+
+    assert np.array_equal(array._data, np.empty((0, 0)))
+    assert np.array_equal(array.lengths, np.array([]))
+
+
+def test_variable_length_array_zero_length_from_list():
+    data = []
+    lengths = np.array([])
+    array = VariableLengthArray(data, lengths)
+
+    assert len(array) == 0
+
+    assert np.array_equal(array._data, np.empty((0, 0)))
+    assert np.array_equal(array.lengths, np.array([]))