Add option to not roll coords

doc/whats-new.rst

@@ -52,6 +52,12 @@ Enhancements
   (:issue:`2331`)
   By `Maximilian Roos <https://github.com/max-sixty>`_.
 
+- You can now control whether or not to offset the coordinates when using
+  the ``roll`` method and the current behavior, coordinates rolled by default,
+  raises a deprecation warning unless explicitly setting the keyword argument.
+  (:issue:`1875`)
+  By `Andrew Huang <https://github.com/ahuang11>`_.
+
 
 Bug fixes
 ~~~~~~~~~

xarray/core/dataarray.py

@@ -2015,14 +2015,20 @@ def shift(self, **shifts):
         variable = self.variable.shift(**shifts)
         return self._replace(variable)
 
-    def roll(self, **shifts):
+    def roll(self, roll_coords=None, **shifts):
         """Roll this array by an offset along one or more dimensions.
 
-        Unlike shift, roll rotates all variables, including coordinates. The
-        direction of rotation is consistent with :py:func:`numpy.roll`.
+        Unlike shift, roll may rotate all variables, including coordinates
+        if specified. The direction of rotation is consistent with
+        :py:func:`numpy.roll`.
 
         Parameters
         ----------
+        roll_coords : bool
+            Indicates whether to  roll the coordinates by the offset
+            The current default of roll_coords (None, equivalent to True) is
+            deprecated and will change to False in a future version.
+            Explicitly pass roll_coords to silence the warning and sort.
         **shifts : keyword arguments of the form {dim: offset}
             Integer offset to rotate each of the given dimensions. Positive
             offsets roll to the right; negative offsets roll to the left.
@@ -2046,7 +2052,7 @@ def roll(self, **shifts):
         Coordinates:
           * x        (x) int64 2 0 1
         """
-        ds = self._to_temp_dataset().roll(**shifts)
+        ds = self._to_temp_dataset().roll(roll_coords=roll_coords, **shifts)
         return self._from_temp_dataset(ds)
 
     @property

xarray/core/dataset.py

@@ -3355,14 +3355,20 @@ def shift(self, **shifts):
 
         return self._replace_vars_and_dims(variables)
 
-    def roll(self, **shifts):
+    def roll(self, roll_coords=None, **shifts):
         """Roll this dataset by an offset along one or more dimensions.
 
-        Unlike shift, roll rotates all variables, including coordinates. The
-        direction of rotation is consistent with :py:func:`numpy.roll`.
+        Unlike shift, roll may rotate all variables, including coordinates
+        if specified. The direction of rotation is consistent with
+        :py:func:`numpy.roll`.
 
         Parameters
         ----------
+        roll_coords : bool
+            Indicates whether to  roll the coordinates by the offset
+            The current default of roll_coords (None, equivalent to True) is
+            deprecated and will change to False in a future version.
+            Explicitly pass roll_coords to silence the warning and sort.
         **shifts : keyword arguments of the form {dim: offset}
             Integer offset to rotate each of the given dimensions. Positive
             offsets roll to the right; negative offsets roll to the left.
@@ -3395,9 +3401,16 @@ def roll(self, **shifts):
 
         variables = OrderedDict()
         for name, var in iteritems(self.variables):
-            var_shifts = dict((k, v) for k, v in shifts.items()
-                              if k in var.dims)
-            variables[name] = var.roll(**var_shifts)
+            if name in self.data_vars or roll_coords:
+                if roll_coords is None:
+                    warnings.warn("roll_coords will be set to False in the future."
+                                  " Explicitly set roll_coords to silence warning.",
+                                   DeprecationWarning, stacklevel=3)
+                var_shifts = dict((k, v) for k, v in shifts.items()
+                                  if k in var.dims)
+                variables[name] = var.roll(**var_shifts)
+            else:
+                variables[name] = var
 
         return self._replace_vars_and_dims(variables)
 

xarray/tests/test_dataset.py

@@ -3837,18 +3837,30 @@ def test_shift(self):
         with raises_regex(ValueError, 'dimensions'):
             ds.shift(foo=123)
 
-    def test_roll(self):
+    def test_roll_coords(self):
         coords = {'bar': ('x', list('abc')), 'x': [-4, 3, 2]}
         attrs = {'meta': 'data'}
         ds = Dataset({'foo': ('x', [1, 2, 3])}, coords, attrs)
-        actual = ds.roll(x=1)
+        actual = ds.roll(x=1, roll_coords=True)
 
         ex_coords = {'bar': ('x', list('cab')), 'x': [2, -4, 3]}
         expected = Dataset({'foo': ('x', [3, 1, 2])}, ex_coords, attrs)
         assert_identical(expected, actual)
 
         with raises_regex(ValueError, 'dimensions'):
-            ds.roll(foo=123)
+            ds.roll(foo=123, roll_coords=True)
+
+    def test_roll_no_coords(self):
+        coords = {'bar': ('x', list('abc')), 'x': [-4, 3, 2]}
+        attrs = {'meta': 'data'}
+        ds = Dataset({'foo': ('x', [1, 2, 3])}, coords, attrs)
+        actual = ds.roll(x=1, roll_coords=False)
+
+        expected = Dataset({'foo': ('x', [3, 1, 2])}, coords, attrs)
+        assert_identical(expected, actual)
+
+        with raises_regex(ValueError, 'dimensions'):
+            ds.roll(abc=321, roll_coords=False)
 
     def test_real_and_imag(self):
         attrs = {'foo': 'bar'}