copy subtrees without creating nodes for ancestors (#201)

* use relative paths for the copied descendants

* check that copying subtrees works

* changelog

Author: keewis

datatree/datatree.py

@@ -734,7 +734,8 @@ def _copy_subtree(
         """Copy entire subtree"""
         new_tree = self._copy_node(deep=deep)
         for node in self.descendants:
-            new_tree[node.path] = node._copy_node(deep=deep)
+            path = node.relative_to(self)
+            new_tree[path] = node._copy_node(deep=deep)
         return new_tree
 
     def _copy_node(

datatree/tests/test_datatree.py

@@ -263,6 +263,14 @@ def test_copy(self, create_test_datatree):
                 assert "foo" not in node.attrs
                 assert node.attrs["Test"] is copied_node.attrs["Test"]
 
+    def test_copy_subtree(self):
+        dt = DataTree.from_dict({"/level1/level2/level3": xr.Dataset()})
+
+        actual = dt["/level1/level2"].copy()
+        expected = DataTree.from_dict({"/level3": xr.Dataset()}, name="level2")
+
+        dtt.assert_identical(actual, expected)
+
     def test_deepcopy(self, create_test_datatree):
         dt = create_test_datatree()
 

docs/source/whats-new.rst

@@ -42,6 +42,8 @@ Bug fixes
 
 - Allow for altering of given dataset inside function called by :py:func:`map_over_subtree` (:issue:`188`, :pull:`194`).
   By `Tom Nicholas <https://github.com/TomNicholas>`_.
+- copy subtrees without creating ancestor nodes (:pull:`201`)
+  By `Justus Magin <https://github.com/keewis>`_.
 
 Documentation
 ~~~~~~~~~~~~~