support constructing Panel or Panel4D with scalar data, fixes pandas-dev#8285

Author: mortada

doc/source/whatsnew/v0.16.0.txt

@@ -622,3 +622,4 @@ Bug Fixes
 - Bug in ``Series.values_counts`` with excluding ``NaN`` for categorical type ``Series`` with ``dropna=True`` (:issue:`9443`)
 
 - Fixed mising numeric_only option for ``DataFrame.std/var/sem`` (:issue:`9201`)
+- Support constructing ``Panel`` or ``Panel4D`` with scalar data (:issue:`8285`)

pandas/core/panel.py

@@ -165,6 +165,13 @@ def _init_data(self, data, copy, dtype, **kwargs):
             mgr = self._init_matrix(data, passed_axes, dtype=dtype, copy=copy)
             copy = False
             dtype = None
+        elif lib.isscalar(data) and all(x is not None for x in passed_axes):
+            if dtype is None:
+                dtype, data = _infer_dtype_from_scalar(data)
+            values = np.empty([len(x) for x in passed_axes], dtype=dtype)
+            values.fill(data)
+            mgr = self._init_matrix(values, passed_axes, dtype=dtype, copy=False)
+            copy = False
         else:  # pragma: no cover
             raise PandasError('Panel constructor not properly called!')
 

pandas/tests/test_panel.py

@@ -888,6 +888,21 @@ def test_constructor(self):
         wp = Panel(vals, copy=True)
         self.assertIsNot(wp.values, vals)
 
+        # GH #8285, test when scalar data is used to construct a Panel
+        # if dtype is not passed, it should be inferred
+        value_and_dtype = [(1, int), (3.14, float), ('foo', np.object_)]
+        for (val, dtype) in value_and_dtype:
+            wp = Panel(val, items=range(2), major_axis=range(3), minor_axis=range(4))
+            vals = np.empty((2, 3, 4), dtype=dtype)
+            vals.fill(val)
+            assert_panel_equal(wp, Panel(vals, dtype=dtype))
+
+        # test the case when dtype is passed
+        wp = Panel(1, items=range(2), major_axis=range(3), minor_axis=range(4), dtype=float)
+        vals = np.empty((2, 3, 4), dtype=float)
+        vals.fill(1)
+        assert_panel_equal(wp, Panel(vals, dtype=float))
+
     def test_constructor_cast(self):
         zero_filled = self.panel.fillna(0)
 

pandas/tests/test_panel4d.py

@@ -629,6 +629,21 @@ def test_constructor(self):
         panel4d = Panel4D(vals, copy=True)
         self.assertIsNot(panel4d.values, vals)
 
+        # GH #8285, test when scalar data is used to construct a Panel4D
+        # if dtype is not passed, it should be inferred
+        value_and_dtype = [(1, int), (3.14, float), ('foo', np.object_)]
+        for (val, dtype) in value_and_dtype:
+            panel4d = Panel4D(val, labels=range(2), items=range(3), major_axis=range(4), minor_axis=range(5))
+            vals = np.empty((2, 3, 4, 5), dtype=dtype)
+            vals.fill(val)
+            assert_panel4d_equal(panel4d, Panel4D(vals, dtype=dtype))
+
+        # test the case when dtype is passed
+        panel4d = Panel4D(1, labels=range(2), items=range(3), major_axis=range(4), minor_axis=range(5), dtype=float)
+        vals = np.empty((2, 3, 4, 5), dtype=float)
+        vals.fill(1)
+        assert_panel4d_equal(panel4d, Panel4D(vals, dtype=float))
+
     def test_constructor_cast(self):
         zero_filled = self.panel4d.fillna(0)