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fix(graphics): ignore sign of scalar in expand_dims, document reversed limits #262

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fix(graphics): ignore sign of scalar in expand_dims, document reversed limits #262

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8 changes: 8 additions & 0 deletions spatialmath/base/graphics.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1708,11 +1708,18 @@ def expand_dims(dim: ArrayLike = None, nd: int = 2) -> NDArray:
* A -> [-A, A, -A, A, -A, A]
* [A,B] -> [A, B, A, B, A, B]
* [A,B,C,D,E,F] -> [A, B, C, D, E, F]

A scalar is symmetric about zero, so its sign is ignored: ``-A`` is the
same as ``A``. For the other forms the values are returned as given and
no ordering check is made. If a minimum is greater than the
corresponding maximum, matplotlib will invert that axis when the limits
are applied, which is a convenient way to flip an axis direction.
"""
dim = smb.getvector(dim)

if nd == 2:
if len(dim) == 1:
dim = abs(dim)
return np.r_[-dim, dim, -dim, dim]
elif len(dim) == 2:
return np.r_[dim[0], dim[1], dim[0], dim[1]]
Expand All @@ -1722,6 +1729,7 @@ def expand_dims(dim: ArrayLike = None, nd: int = 2) -> NDArray:
raise ValueError("bad dimension specified")
elif nd == 3:
if len(dim) == 1:
dim = abs(dim)
return np.r_[-dim, dim, -dim, dim, -dim, dim]
elif len(dim) == 2:
return np.r_[dim[0], dim[1], dim[0], dim[1], dim[0], dim[1]]
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17 changes: 17 additions & 0 deletions tests/base/test_graphics.py
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Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,23 @@ class TestGraphics(unittest.TestCase):
def teardown_method(self, method):
plt.close("all")

def test_expand_dims(self):
np.testing.assert_array_equal(expand_dims(3), [-3, 3, -3, 3])
np.testing.assert_array_equal(expand_dims(-3), [-3, 3, -3, 3])
np.testing.assert_array_equal(expand_dims([1, 2]), [1, 2, 1, 2])
np.testing.assert_array_equal(expand_dims([1, 2, 3, 4]), [1, 2, 3, 4])
# reversed limits are passed through, matplotlib inverts the axis
np.testing.assert_array_equal(expand_dims([2, 1]), [2, 1, 2, 1])

np.testing.assert_array_equal(expand_dims(-3, nd=3), [-3, 3, -3, 3, -3, 3])
np.testing.assert_array_equal(expand_dims([1, 2], nd=3), [1, 2] * 3)
np.testing.assert_array_equal(expand_dims([1, 2, 3, 4, 5, 6], nd=3), [1, 2, 3, 4, 5, 6])

with self.assertRaises(ValueError):
expand_dims([1, 2, 3])
with self.assertRaises(ValueError):
expand_dims([1, 2, 3, 4], nd=3)

@pytest.mark.skipif(
sys.platform.startswith("darwin") and sys.version_info < (3, 11),
reason="tkinter bug with mac",
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