From c472f8a4c79f872edb9dcd7825f786ecb9aff5c0 Mon Sep 17 00:00:00 2001
From: ellesmith88 <40183561+ellesmith88@users.noreply.github.com>
Date: Thu, 1 Jul 2021 16:50:33 +0100
Subject: [PATCH] Allow user to explicitly disable coordinates attribute
 (#5514)

---
 doc/whats-new.rst                |  3 +++
 xarray/conventions.py            | 12 +++++++++++
 xarray/tests/test_conventions.py | 34 ++++++++++++++++++++++++++++++++
 3 files changed, 49 insertions(+)

diff --git a/doc/whats-new.rst b/doc/whats-new.rst
index 57ec853915b..daddc91b73f 100644
--- a/doc/whats-new.rst
+++ b/doc/whats-new.rst
@@ -48,6 +48,9 @@ New Features
   By `Justus Magin <https://github.com/keewis>`_.
 - Allow plotting categorical data (:pull:`5464`).
   By `Jimmy Westling <https://github.com/illviljan>`_.
+- Allow removal of the coordinate attribute ``coordinates`` on variables by setting ``.attrs['coordinates']= None``
+  (:issue:`5510`).
+  By `Elle Smith <https://github.com/ellesmith88>`_.
 
 Breaking changes
 ~~~~~~~~~~~~~~~~
diff --git a/xarray/conventions.py b/xarray/conventions.py
index 901d19bd99b..c3a05e42f82 100644
--- a/xarray/conventions.py
+++ b/xarray/conventions.py
@@ -751,6 +751,18 @@ def _encode_coordinates(variables, attributes, non_dim_coord_names):
                 f"'coordinates' found in both attrs and encoding for variable {name!r}."
             )
 
+        # if coordinates set to None, don't write coordinates attribute
+        if (
+            "coordinates" in attrs
+            and attrs.get("coordinates") is None
+            or "coordinates" in encoding
+            and encoding.get("coordinates") is None
+        ):
+            # make sure "coordinates" is removed from attrs/encoding
+            attrs.pop("coordinates", None)
+            encoding.pop("coordinates", None)
+            continue
+
         # this will copy coordinates from encoding to attrs if "coordinates" in attrs
         # after the next line, "coordinates" is never in encoding
         # we get support for attrs["coordinates"] for free.
diff --git a/xarray/tests/test_conventions.py b/xarray/tests/test_conventions.py
index cd8e3419231..ceea167719f 100644
--- a/xarray/tests/test_conventions.py
+++ b/xarray/tests/test_conventions.py
@@ -142,6 +142,40 @@ def test_do_not_overwrite_user_coordinates(self):
         with pytest.raises(ValueError, match=r"'coordinates' found in both attrs"):
             conventions.encode_dataset_coordinates(orig)
 
+    def test_emit_coordinates_attribute_in_attrs(self):
+        orig = Dataset(
+            {"a": 1, "b": 1},
+            coords={"t": np.array("2004-11-01T00:00:00", dtype=np.datetime64)},
+        )
+
+        orig["a"].attrs["coordinates"] = None
+        enc, _ = conventions.encode_dataset_coordinates(orig)
+
+        # check coordinate attribute emitted for 'a'
+        assert "coordinates" not in enc["a"].attrs
+        assert "coordinates" not in enc["a"].encoding
+
+        # check coordinate attribute not emitted for 'b'
+        assert enc["b"].attrs.get("coordinates") == "t"
+        assert "coordinates" not in enc["b"].encoding
+
+    def test_emit_coordinates_attribute_in_encoding(self):
+        orig = Dataset(
+            {"a": 1, "b": 1},
+            coords={"t": np.array("2004-11-01T00:00:00", dtype=np.datetime64)},
+        )
+
+        orig["a"].encoding["coordinates"] = None
+        enc, _ = conventions.encode_dataset_coordinates(orig)
+
+        # check coordinate attribute emitted for 'a'
+        assert "coordinates" not in enc["a"].attrs
+        assert "coordinates" not in enc["a"].encoding
+
+        # check coordinate attribute not emitted for 'b'
+        assert enc["b"].attrs.get("coordinates") == "t"
+        assert "coordinates" not in enc["b"].encoding
+
     @requires_dask
     def test_string_object_warning(self):
         original = Variable(("x",), np.array(["foo", "bar"], dtype=object)).chunk()