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allow DataTree objects as root node in from_dict #221

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allow DataTree objects as root node in from_dict #221

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2da3a7d
verify that `from_dict` allows having a `DataTree` object in `"/"`
keewis Feb 28, 2023
9d4317e
copy the root node if it is already a `DataTree` object
keewis Feb 28, 2023
5a6b3d1
changelog
keewis Feb 28, 2023
842f657
Merge branch 'main' into from_dict-root
TomNicholas Oct 23, 2023
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5 changes: 4 additions & 1 deletion datatree/datatree.py
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Original file line number Diff line number Diff line change
Expand Up @@ -991,7 +991,10 @@ def from_dict(

# First create the root node
root_data = d.pop("/", None)
obj = cls(name=name, data=root_data, parent=None, children=None)
if not isinstance(root_data, cls):
obj = cls(name=name, data=root_data, parent=None, children=None)
else:
obj = root_data.copy()
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I think there is potential for bugs here - .copy() will copy child nodes too, so if root_data has children already they will presumably be copied into the new tree. You could also then double-specify the contents of a single node, once as the child of the root and again in the supplied dict.

In fact your previous PR might do this too - I think we should decide what we want the behavior to be: either drop all children of supplied nodes or explicitly test that we keep children too.

If we do want to drop the children it would probably be clearer to just create a new node using a copy of the supplied node's name and data.

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this is a bit similar to what xarray does already when passing DataArray objects with coordinates to the Dataset constructor / Dataset.assign*: those coordinates will be carried over (unintentionally overriding coordinates explicitly passed in the same call).

I'm not sure if we need to copy the behavior, though.

I didn't have a need for it ever since opening this PR, so this is also pretty low-priority for me (as you might have guessed from the long delay)


if d:
# Populate tree with children determined from data_objects mapping
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7 changes: 7 additions & 0 deletions datatree/tests/test_datatree.py
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Expand Up @@ -499,6 +499,13 @@ def test_datatree_values(self):

dtt.assert_identical(actual, expected)

def test_datatree_values_root(self):
expected = DataTree(data=xr.Dataset({"a": 1}))

actual = DataTree.from_dict({"/": expected})

dtt.assert_identical(actual, expected)

def test_roundtrip(self, simple_datatree):
dt = simple_datatree
roundtrip = DataTree.from_dict(dt.to_dict())
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2 changes: 2 additions & 0 deletions docs/source/whats-new.rst
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Expand Up @@ -70,6 +70,8 @@ Bug fixes
By `Tom Nicholas <https://github.com/TomNicholas>`_.
- copy subtrees without creating ancestor nodes (:pull:`201`)
By `Justus Magin <https://github.com/keewis>`_.
- allow `DataTree` objects as root node in `from_dict` (:pull:`221`)
By `Justus Magin <https://github.com/keewis>`_.

Documentation
~~~~~~~~~~~~~
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