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raise informative error message on misshapen input to set_offsets #22408

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raise informative error message on misshapen input to set_offsets #22408

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ea70652
allow setting collection offsets to empty
ianhi Feb 5, 2022
133019a
don't change input - give informative error message
ianhi Dec 12, 2025
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10 changes: 10 additions & 0 deletions lib/matplotlib/collections.py
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Original file line number Diff line number Diff line change
Expand Up @@ -630,6 +630,16 @@ def set_offsets(self, offsets):
offsets = np.asanyarray(offsets)
if offsets.shape == (2,): # Broadcast (2,) -> (1, 2) but nothing else.
offsets = offsets[None, :]
if offsets.ndim != 2 or offsets.shape[1] != 2:
if offsets.shape == (2, 0):
raise ValueError(
"offsets must have shape (N, 2), got (2, 0). "
"If you want an empty collection, use "
"np.column_stack([[], []]) or np.empty((0, 2))."
)
raise ValueError(
f"offsets must have shape (N, 2), or (2,) got {offsets.shape}."
)
cstack = (np.ma.column_stack if isinstance(offsets, np.ma.MaskedArray)
else np.column_stack)
self._offsets = cstack(
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34 changes: 34 additions & 0 deletions lib/matplotlib/tests/test_collections.py
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Expand Up @@ -1314,6 +1314,40 @@ def test_set_offset_units():
np.testing.assert_allclose(off0, sc.get_offsets())


def test_set_offset_empty():
# Test with (0, 2) shaped array (the correct empty shape per (N, 2) docs)
# Using np.zeros((0, 2))
modified = mcollections.Collection(offsets=np.column_stack([[0, 1], [0, 1]]))
modified.set_offsets(np.zeros((0, 2)))
assert modified.get_offsets().shape == (0, 2)

# Using np.column_stack([[], []])
modified2 = mcollections.Collection(offsets=np.column_stack([[0, 1], [0, 1]]))
modified2.set_offsets(np.column_stack([[], []]))
assert modified2.get_offsets().shape == (0, 2)


def test_set_offset_wrong_shape_error():
# Test that arrays with wrong shape raise an error
coll = mcollections.Collection(offsets=np.column_stack([[0, 1], [0, 1]]))

# Wrong ndim
with pytest.raises(ValueError, match=r"offsets must have shape \(N, 2\)"):
coll.set_offsets([1, 2, 3]) # (3,) - wrong ndim
with pytest.raises(ValueError, match=r"offsets must have shape \(N, 2\)"):
coll.set_offsets([[[1, 2]]]) # (1, 1, 2) - 3D array

# Wrong second dimension
with pytest.raises(ValueError, match=r"use np.column_stack"):
coll.set_offsets([[], []]) # (2, 0) - special error with suggestion
with pytest.raises(ValueError, match=r"offsets must have shape \(N, 2\)"):
coll.set_offsets([[1], [2]]) # (2, 1)
with pytest.raises(ValueError, match=r"offsets must have shape \(N, 2\)"):
coll.set_offsets([[1, 2, 3], [4, 5, 6]]) # (2, 3)
with pytest.raises(ValueError, match=r"offsets must have shape \(N, 2\)"):
coll.set_offsets([[1, 2, 3], [4, 5, 6], [7, 8, 9]]) # (3, 3)


@image_comparison(baseline_images=["test_check_masked_offsets"],
extensions=["png"], remove_text=True, style="mpl20")
def test_check_masked_offsets():
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