Initialize empty or full DataArray

doc/whats-new.rst

@@ -60,6 +60,9 @@ Enhancements
 - In :py:meth:`~xarray.Dataset.to_zarr`, passing ``mode`` is not mandatory if
   ``append_dim`` is set, as it will automatically be set to ``'a'`` internally.
   By `David Brochart <https://github.com/davidbrochart>`_.
+- Added the ability to initialize an empty or full DataArray
+  with a single value. (:issue:`277`)
+  By `Gerardo Rivera <http://github.com/dangomelon>`_.
 
 Bug fixes
 ~~~~~~~~~

xarray/core/dataarray.py

@@ -158,6 +158,28 @@ def _infer_coords_and_dims(
     return new_coords, dims
 
 
+def _check_data_shape(data, coords, dims):
+    if data is dtypes.NA:
+        data = np.nan
+    if (
+        coords is not None
+        and utils.is_scalar(data, include_0d=False)
+        and not isinstance(data, indexing.ExplicitlyIndexed)
+    ):
+        if utils.is_dict_like(coords):
+            if dims is None:
+                return data
+            else:
+                data_shape = tuple(
+                    as_variable(coords[k], k).size if k in coords.keys() else 1
+                    for k in dims
+                )
+        else:
+            data_shape = tuple(as_variable(coord, "foo").size for coord in coords)
+        data = np.full(data_shape, data)
+    return data
+
+
 class _LocIndexer:
     def __init__(self, data_array: "DataArray"):
         self.data_array = data_array
@@ -234,7 +256,7 @@ class DataArray(AbstractArray, DataWithCoords):
 
     def __init__(
         self,
-        data: Any,
+        data: Any = dtypes.NA,
         coords: Union[Sequence[Tuple], Mapping[Hashable, Any], None] = None,
         dims: Union[Hashable, Sequence[Hashable], None] = None,
         name: Hashable = None,
@@ -323,6 +345,7 @@ def __init__(
             if encoding is None:
                 encoding = getattr(data, "encoding", None)
 
+            data = _check_data_shape(data, coords, dims)
             data = as_compatible_data(data)
             coords, dims = _infer_coords_and_dims(data.shape, coords, dims)
             variable = Variable(dims, data, attrs, encoding, fastpath=True)

xarray/core/utils.py

@@ -272,13 +272,15 @@ def either_dict_or_kwargs(
         return cast(Mapping[Hashable, T], kw_kwargs)
 
 
-def is_scalar(value: Any) -> bool:
+def is_scalar(value: Any, include_0d: bool = True) -> bool:
     """Whether to treat a value as a scalar.
 
     Any non-iterable, string, or 0-D array
     """
+    if include_0d:
+        include_0d = getattr(value, "ndim", None) == 0
     return (
-        getattr(value, "ndim", None) == 0
+        include_0d
         or isinstance(value, (str, bytes))
         or not (
             isinstance(value, (Iterable,) + dask_array_type)

xarray/tests/test_dataarray.py

@@ -1506,6 +1506,27 @@ def test_rename(self):
         renamed_kwargs = self.dv.x.rename(x="z").rename("z")
         assert_identical(renamed, renamed_kwargs)
 
+    def test_init_value(self):
+        expected = DataArray(
+            np.full((3, 4), 3), dims=["x", "y"], coords=[range(3), range(4)]
+        )
+        actual = DataArray(3, dims=["x", "y"], coords=[range(3), range(4)])
+        assert_identical(expected, actual)
+
+        expected = DataArray(
+            np.full((1, 10, 2), 0),
+            dims=["w", "x", "y"],
+            coords={"x": np.arange(10), "y": ["north", "south"]},
+        )
+        actual = DataArray(0, dims=expected.dims, coords=expected.coords)
+        assert_identical(expected, actual)
+
+        expected = DataArray(
+            np.full((10, 2), np.nan), coords=[("x", np.arange(10)), ("y", ["a", "b"])]
+        )
+        actual = DataArray(coords=[("x", np.arange(10)), ("y", ["a", "b"])])
+        assert_identical(expected, actual)
+
     def test_swap_dims(self):
         array = DataArray(np.random.randn(3), {"y": ("x", list("abc"))}, "x")
         expected = DataArray(array.values, {"y": list("abc")}, dims="y")