Allow ellipsis (...) in transpose (#3421)

* infix_dims function

* implement transpose with ellipsis

* also infix in dataarray

* check errors centrally, remove boilerplate from transpose methods

* whatsnew

* docs

* remove old comments

* generator->iterator

* test for differently ordered dimensions

doc/reshaping.rst

@@ -18,12 +18,14 @@ Reordering dimensions
 ---------------------
 
 To reorder dimensions on a :py:class:`~xarray.DataArray` or across all variables
-on a :py:class:`~xarray.Dataset`, use :py:meth:`~xarray.DataArray.transpose`:
+on a :py:class:`~xarray.Dataset`, use :py:meth:`~xarray.DataArray.transpose`. An 
+ellipsis (`...`) can be use to represent all other dimensions:
 
 .. ipython:: python
 
     ds = xr.Dataset({'foo': (('x', 'y', 'z'), [[[42]]]), 'bar': (('y', 'z'), [[24]])})
     ds.transpose('y', 'z', 'x')
+    ds.transpose(..., 'x')  # equivalent
     ds.transpose()  # reverses all dimensions
 
 Expand and squeeze dimensions

doc/whats-new.rst

@@ -25,6 +25,10 @@ Breaking changes
 
 New Features
 ~~~~~~~~~~~~
+- :py:meth:`Dataset.transpose` and :py:meth:`DataArray.transpose` now support an ellipsis (`...`)
+  to represent all 'other' dimensions. For example, to move one dimension to the front,
+  use `.transpose('x', ...)`. (:pull:`3421`)
+  By `Maximilian Roos <https://github.com/max-sixty>`_
 - Changed `xr.ALL_DIMS` to equal python's `Ellipsis` (`...`), and changed internal usages to use
   `...` directly. As before, you can use this to instruct a `groupby` operation
   to reduce over all dimensions. While we have no plans to remove `xr.ALL_DIMS`, we suggest

setup.cfg

@@ -117,4 +117,7 @@ tag_prefix = v
 parentdir_prefix = xarray-
 
 [aliases]
-test = pytest
+test = pytest
+
+[pytest-watch]
+nobeep = True

xarray/core/dataarray.py

@@ -1863,12 +1863,7 @@ def transpose(self, *dims: Hashable, transpose_coords: bool = None) -> "DataArra
         Dataset.transpose
         """
         if dims:
-            if set(dims) ^ set(self.dims):
-                raise ValueError(
-                    "arguments to transpose (%s) must be "
-                    "permuted array dimensions (%s)" % (dims, tuple(self.dims))
-                )
-
+            dims = tuple(utils.infix_dims(dims, self.dims))
         variable = self.variable.transpose(*dims)
         if transpose_coords:
             coords: Dict[Hashable, Variable] = {}

xarray/core/dataset.py

@@ -3712,14 +3712,14 @@ def transpose(self, *dims: Hashable) -> "Dataset":
         DataArray.transpose
         """
         if dims:
-            if set(dims) ^ set(self.dims):
+            if set(dims) ^ set(self.dims) and ... not in dims:
                 raise ValueError(
                     "arguments to transpose (%s) must be "
                     "permuted dataset dimensions (%s)" % (dims, tuple(self.dims))
                 )
         ds = self.copy()
         for name, var in self._variables.items():
-            var_dims = tuple(dim for dim in dims if dim in var.dims)
+            var_dims = tuple(dim for dim in dims if dim in (var.dims + (...,)))
             ds._variables[name] = var.transpose(*var_dims)
         return ds
 

xarray/core/utils.py

@@ -10,6 +10,7 @@
     AbstractSet,
     Any,
     Callable,
+    Collection,
     Container,
     Dict,
     Hashable,
@@ -660,6 +661,30 @@ def __len__(self) -> int:
         return len(self._data) - num_hidden
 
 
+def infix_dims(dims_supplied: Collection, dims_all: Collection) -> Iterator:
+    """
+    Resolves a supplied list containing an ellispsis representing other items, to
+    a generator with the 'realized' list of all items
+    """
+    if ... in dims_supplied:
+        if len(set(dims_all)) != len(dims_all):
+            raise ValueError("Cannot use ellipsis with repeated dims")
+        if len([d for d in dims_supplied if d == ...]) > 1:
+            raise ValueError("More than one ellipsis supplied")
+        other_dims = [d for d in dims_all if d not in dims_supplied]
+        for d in dims_supplied:
+            if d == ...:
+                yield from other_dims
+            else:
+                yield d
+    else:
+        if set(dims_supplied) ^ set(dims_all):
+            raise ValueError(
+                f"{dims_supplied} must be a permuted list of {dims_all}, unless `...` is included"
+            )
+        yield from dims_supplied
+
+
 def get_temp_dimname(dims: Container[Hashable], new_dim: Hashable) -> Hashable:
     """ Get an new dimension name based on new_dim, that is not used in dims.
     If the same name exists, we add an underscore(s) in the head.

xarray/core/variable.py

@@ -25,6 +25,7 @@
     OrderedSet,
     decode_numpy_dict_values,
     either_dict_or_kwargs,
+    infix_dims,
     ensure_us_time_resolution,
 )
 
@@ -1228,6 +1229,7 @@ def transpose(self, *dims) -> "Variable":
         """
         if len(dims) == 0:
             dims = self.dims[::-1]
+        dims = tuple(infix_dims(dims, self.dims))
         axes = self.get_axis_num(dims)
         if len(dims) < 2:  # no need to transpose if only one dimension
             return self.copy(deep=False)

xarray/tests/__init__.py

@@ -158,18 +158,21 @@ def source_ndarray(array):
 
 
 def assert_equal(a, b):
+    __tracebackhide__ = True
     xarray.testing.assert_equal(a, b)
     xarray.testing._assert_internal_invariants(a)
     xarray.testing._assert_internal_invariants(b)
 
 
 def assert_identical(a, b):
+    __tracebackhide__ = True
     xarray.testing.assert_identical(a, b)
     xarray.testing._assert_internal_invariants(a)
     xarray.testing._assert_internal_invariants(b)
 
 
 def assert_allclose(a, b, **kwargs):
+    __tracebackhide__ = True
     xarray.testing.assert_allclose(a, b, **kwargs)
     xarray.testing._assert_internal_invariants(a)
     xarray.testing._assert_internal_invariants(b)

xarray/tests/test_dataarray.py

@@ -2068,6 +2068,10 @@ def test_transpose(self):
         )
         assert_equal(expected, actual)
 
+        # same as previous but with ellipsis
+        actual = da.transpose("z", ..., "x", transpose_coords=True)
+        assert_equal(expected, actual)
+
         with pytest.raises(ValueError):
             da.transpose("x", "y")
 

xarray/tests/test_dataset.py

@@ -4675,6 +4675,10 @@ def test_dataset_transpose(self):
         )
         assert_identical(expected, actual)
 
+        actual = ds.transpose(...)
+        expected = ds
+        assert_identical(expected, actual)
+
         actual = ds.transpose("x", "y")
         expected = ds.apply(lambda x: x.transpose("x", "y", transpose_coords=True))
         assert_identical(expected, actual)
@@ -4690,13 +4694,32 @@ def test_dataset_transpose(self):
             expected_dims = tuple(d for d in new_order if d in ds[k].dims)
             assert actual[k].dims == expected_dims
 
-        with raises_regex(ValueError, "arguments to transpose"):
+        # same as above but with ellipsis
+        new_order = ("dim2", "dim3", "dim1", "time")
+        actual = ds.transpose("dim2", "dim3", ...)
+        for k in ds.variables:
+            expected_dims = tuple(d for d in new_order if d in ds[k].dims)
+            assert actual[k].dims == expected_dims
+
+        with raises_regex(ValueError, "permuted"):
             ds.transpose("dim1", "dim2", "dim3")
-        with raises_regex(ValueError, "arguments to transpose"):
+        with raises_regex(ValueError, "permuted"):
             ds.transpose("dim1", "dim2", "dim3", "time", "extra_dim")
 
         assert "T" not in dir(ds)
 
+    def test_dataset_ellipsis_transpose_different_ordered_vars(self):
+        # https://github.com/pydata/xarray/issues/1081#issuecomment-544350457
+        ds = Dataset(
+            dict(
+                a=(("w", "x", "y", "z"), np.ones((2, 3, 4, 5))),
+                b=(("x", "w", "y", "z"), np.zeros((3, 2, 4, 5))),
+            )
+        )
+        result = ds.transpose(..., "z", "y")
+        assert list(result["a"].dims) == list("wxzy")
+        assert list(result["b"].dims) == list("xwzy")
+
     def test_dataset_retains_period_index_on_transpose(self):
 
         ds = create_test_data()

xarray/tests/test_utils.py

@@ -275,3 +275,27 @@ def test_either_dict_or_kwargs():
 
     with pytest.raises(ValueError, match=r"foo"):
         result = either_dict_or_kwargs(dict(a=1), dict(a=1), "foo")
+
+
+@pytest.mark.parametrize(
+    ["supplied", "all_", "expected"],
+    [
+        (list("abc"), list("abc"), list("abc")),
+        (["a", ..., "c"], list("abc"), list("abc")),
+        (["a", ...], list("abc"), list("abc")),
+        (["c", ...], list("abc"), list("cab")),
+        ([..., "b"], list("abc"), list("acb")),
+        ([...], list("abc"), list("abc")),
+    ],
+)
+def test_infix_dims(supplied, all_, expected):
+    result = list(utils.infix_dims(supplied, all_))
+    assert result == expected
+
+
+@pytest.mark.parametrize(
+    ["supplied", "all_"], [([..., ...], list("abc")), ([...], list("aac"))]
+)
+def test_infix_dims_errors(supplied, all_):
+    with pytest.raises(ValueError):
+        list(utils.infix_dims(supplied, all_))

xarray/tests/test_variable.py

@@ -1280,6 +1280,9 @@ def test_transpose(self):
         w2 = Variable(["d", "b", "c", "a"], np.einsum("abcd->dbca", x))
         assert w2.shape == (5, 3, 4, 2)
         assert_identical(w2, w.transpose("d", "b", "c", "a"))
+        assert_identical(w2, w.transpose("d", ..., "a"))
+        assert_identical(w2, w.transpose("d", "b", "c", ...))
+        assert_identical(w2, w.transpose(..., "b", "c", "a"))
         assert_identical(w, w2.transpose("a", "b", "c", "d"))
         w3 = Variable(["b", "c", "d", "a"], np.einsum("abcd->bcda", x))
         assert_identical(w, w3.transpose("a", "b", "c", "d"))