Jul 17, 2025 · Jul 17, 2025
diff --git a/lib/matplotlib/axes/_base.py b/lib/matplotlib/axes/_base.py
                # the call so that self.dataLim will update its own minpos.
                # This ensures that log scales see the correct minimum.
                points = np.concatenate([points, [datalim.minpos]])
            self.update_datalim(points)
            # only update the dataLim for x/y if the collection uses transData
            # in this direction.
            updatex, updatey = (collection.get_transform()
                                .contains_branch_seperately(self.transData))
            self.update_datalim(points, updatex=updatex, updatey=updatey)

        self.stale = True
        return collection
diff --git a/lib/matplotlib/tests/test_collections.py b/lib/matplotlib/tests/test_collections.py


 def test_blended_collection_autolim():
    a = [1, 2, 4]
    height = .2
    f, ax = plt.subplots()

    xy_pairs = np.column_stack([np.repeat(a, 2), np.tile([0, height], len(a))])
    line_segs = xy_pairs.reshape([len(a), 2, 2])
    # sample data to give initial data limits
    ax.plot([2, 3, 4], [0.4, 0.6, 0.5])
    np.testing.assert_allclose((ax.dataLim.xmin, ax.dataLim.xmax), (2, 4))
    data_ymin, data_ymax = ax.dataLim.ymin, ax.dataLim.ymax

    f, ax = plt.subplots()
    # LineCollection with vertical lines spanning the Axes vertical, using transAxes
    x = [1, 2, 3, 4, 5]
    vertical_lines = [np.array([[xi, 0], [xi, 1]]) for xi in x]
    trans = mtransforms.blended_transform_factory(ax.transData, ax.transAxes)
    ax.add_collection(LineCollection(line_segs, transform=trans))
    ax.autoscale_view(scalex=True, scaley=False)
    np.testing.assert_allclose(ax.get_xlim(), [1., 4.])
    ax.add_collection(LineCollection(vertical_lines, transform=trans))

    # check that the x data limits are updated to include the LineCollection
    np.testing.assert_allclose((ax.dataLim.xmin, ax.dataLim.xmax), (1, 5))
    # check that the y data limits are not updated (because they are not transData)
    np.testing.assert_allclose((ax.dataLim.ymin, ax.dataLim.ymax), (0.4, 0.6))


 def test_singleton_autolim():
Original file line number	Diff line number	Diff line change
Expand Up		@@ -2361,7 +2361,11 @@ def add_collection(self, collection, autolim=True):
		# the call so that self.dataLim will update its own minpos.
		# This ensures that log scales see the correct minimum.
		points = np.concatenate([points, [datalim.minpos]])
		self.update_datalim(points)
		# only update the dataLim for x/y if the collection uses transData
		# in this direction.
		updatex, updatey = (collection.get_transform()
		.contains_branch_seperately(self.transData))
		self.update_datalim(points, updatex=updatex, updatey=updatey)

		self.stale = True
		return collection
Expand Down
Original file line number	Diff line number	Diff line change
Expand Up		@@ -899,17 +899,23 @@ def test_collection_set_array():


		def test_blended_collection_autolim():
		a = [1, 2, 4]
		height = .2
		f, ax = plt.subplots()

		xy_pairs = np.column_stack([np.repeat(a, 2), np.tile([0, height], len(a))])
		line_segs = xy_pairs.reshape([len(a), 2, 2])
		# sample data to give initial data limits
		ax.plot([2, 3, 4], [0.4, 0.6, 0.5])
		np.testing.assert_allclose((ax.dataLim.xmin, ax.dataLim.xmax), (2, 4))
		data_ymin, data_ymax = ax.dataLim.ymin, ax.dataLim.ymax

		f, ax = plt.subplots()
		# LineCollection with vertical lines spanning the Axes vertical, using transAxes
		x = [1, 2, 3, 4, 5]
		vertical_lines = [np.array([[xi, 0], [xi, 1]]) for xi in x]
		trans = mtransforms.blended_transform_factory(ax.transData, ax.transAxes)
		ax.add_collection(LineCollection(line_segs, transform=trans))
		ax.autoscale_view(scalex=True, scaley=False)
		np.testing.assert_allclose(ax.get_xlim(), [1., 4.])
		ax.add_collection(LineCollection(vertical_lines, transform=trans))

		# check that the x data limits are updated to include the LineCollection
		np.testing.assert_allclose((ax.dataLim.xmin, ax.dataLim.xmax), (1, 5))
		# check that the y data limits are not updated (because they are not transData)
		np.testing.assert_allclose((ax.dataLim.ymin, ax.dataLim.ymax), (0.4, 0.6))
Comment on lines +904 to +918 Copy link MemberAuthor timhoffmJul 17, 2025 Choose a reason for hiding this comment The reason will be displayed to describe this comment to others.Learn more. Note 1: Before, the test did only check that the x data limits were expanded. It did not investigate the y data limits. Now it also ensures, that y data limits are not changed. Note 2: I've switched from testing view limits to testing data limits, because that's the relevant quantity autolim influences. We save the`autoscale_view()` by not looking at the view limits.


		def test_singleton_autolim():
Expand Down