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Add DataTree.move to move a node to another place #9442

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Add DataTree.move to move a node to another place #9442

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44 changes: 44 additions & 0 deletions xarray/core/datatree.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1060,6 +1060,50 @@ def drop_nodes(
result._replace_node(children=children_to_keep)
return result

def move(self, origin: str, destination: str, parents: bool = False) -> DataTree:
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There's another possible way of writing this method: dt.move(destination) where it's assumed that the origin is the current node, and the returned result is the root of the new tree.

But I think your way is probably the less surprising of the two.

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I see. Should we do both, or would that be too confusing?

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I think your way is fine! I just wanted to comment to point this out for posterity :)

"""
Move a node to a different location in the tree.

Parameters
----------
origin: str
The node to move.
destination: str
The new node destination.
parents: bool, optional
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I think this argument should be renamed, though I'm not sure what to. Perhaps create_intermediates?

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I am not sure either, I took inspiration from pathlib: https://docs.python.org/3/library/pathlib.html#pathlib.Path.mkdir
Happy to change to anything.

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Ah I see. Taking inspiration from pathlib was a good idea. But I don't think it's a great name in this case...

The exists_ok arg in pathlib.Path.mkdir is also potentially relevant - the user might want to avoid replacing the subtree already at that path.

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Ah, good point. I will add an exists_ok argument for now, until we settle on names for these arguments.

If `parents` is `True`, create the additional paths needed to reach the
destination. Otherwise, raise an error. Set to `False` by default.

Returns
-------
DataTree
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Suggested change
DataTree
DataTree
Copied subtree with the node moved.


Examples
--------
>>> dt = DataTree.from_dict(
... {
... "/to_move/A": None,
... "/to_move/B": None,
... "/destination/other": None,
... }
... )
>>> dt.move("to_move", "destination")
<xarray.DataTree>
Group: /
└── Group: /destination
├── Group: /destination/other
└── Group: /destination/to_move
├── Group: /destination/to_move/A
└── Group: /destination/to_move/B
"""
result = self.copy()
to_move = result[origin]
to_move.orphan()
result._set_item(
f"{destination}/{to_move.name}", to_move, new_nodes_along_path=parents
)
return result

@classmethod
def from_dict(
cls,
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35 changes: 35 additions & 0 deletions xarray/tests/test_datatree.py
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Original file line number Diff line number Diff line change
Expand Up @@ -972,6 +972,41 @@ def test_assign(self):
result = dt.assign({"foo": xr.DataArray(0), "a": DataTree()})
assert_equal(result, expected)

def test_move(self):
dt = DataTree.from_dict(
{"/to_move/A": None, "/to_move/B": None, "/destination/other": None}
)
result = dt.move("to_move", "destination")
expected = DataTree.from_dict(
{
"/destination/to_move/A": None,
"/destination/to_move/B": None,
"/destination/other": None,
}
)
assert_equal(result, expected)

def test_move_no_parents(self):
dt = DataTree.from_dict(
{"/to_move/A": None, "/to_move/B": None, "/destination/other": None}
)
with pytest.raises(KeyError, match="Could not reach node"):
dt.move("to_move", "destination/deep/down")

def test_move_parents(self):
dt = DataTree.from_dict(
{"/to_move/A": None, "/to_move/B": None, "/destination/other": None}
)
result = dt.move("to_move", "destination/deep/down", parents=True)
expected = DataTree.from_dict(
{
"/destination/deep/down/to_move/A": None,
"/destination/deep/down/to_move/B": None,
"/destination/other": None,
}
)
assert_equal(result, expected)


class TestPipe:
def test_noop(self, create_test_datatree):
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