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MNT: Remove auto-flattening of input data to pcolormesh #24638

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Merged
merged 1 commit into from
Jan 30, 2023
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MNT: Remove auto-flattening of input data to pcolormesh #24638

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3 changes: 0 additions & 3 deletions lib/matplotlib/axes/_axes.py
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Original file line number Diff line number Diff line change
Expand Up @@ -6220,9 +6220,6 @@ def pcolormesh(self, *args, alpha=None, norm=None, cmap=None, vmin=None,
X, Y, C, shading = self._pcolorargs('pcolormesh', *args,
shading=shading, kwargs=kwargs)
coords = np.stack([X, Y], axis=-1)
# convert to one dimensional array, except for 3D RGB(A) arrays
if C.ndim != 3:
C = C.ravel()

kwargs.setdefault('snap', mpl.rcParams['pcolormesh.snap'])

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32 changes: 16 additions & 16 deletions lib/matplotlib/tests/test_collections.py
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Original file line number Diff line number Diff line change
Expand Up @@ -914,13 +914,13 @@ def test_quadmesh_vmin_vmax():
norm = mpl.colors.Normalize(vmin=0, vmax=1)
coll = ax.pcolormesh([[1]], cmap=cmap, norm=norm)
fig.canvas.draw()
assert np.array_equal(coll.get_facecolors()[0, :], cmap(norm(1)))
assert np.array_equal(coll.get_facecolors()[0, 0, :], cmap(norm(1)))

# Change the vmin/vmax of the norm so that the color is from
# the bottom of the colormap now
norm.vmin, norm.vmax = 1, 2
fig.canvas.draw()
assert np.array_equal(coll.get_facecolors()[0, :], cmap(norm(1)))
assert np.array_equal(coll.get_facecolors()[0, 0, :], cmap(norm(1)))


def test_quadmesh_alpha_array():
Expand All @@ -935,16 +935,16 @@ def test_quadmesh_alpha_array():
coll2 = ax1.pcolormesh(x, y, z)
coll2.set_alpha(alpha)
plt.draw()
assert_array_equal(coll1.get_facecolors()[:, -1], alpha_flat)
assert_array_equal(coll2.get_facecolors()[:, -1], alpha_flat)
assert_array_equal(coll1.get_facecolors()[..., -1], alpha)
assert_array_equal(coll2.get_facecolors()[..., -1], alpha)
# Or provide 1-D alpha:
fig, (ax0, ax1) = plt.subplots(2)
coll1 = ax0.pcolormesh(x, y, z, alpha=alpha_flat)
coll1 = ax0.pcolormesh(x, y, z, alpha=alpha)
coll2 = ax1.pcolormesh(x, y, z)
coll2.set_alpha(alpha_flat)
coll2.set_alpha(alpha)
plt.draw()
assert_array_equal(coll1.get_facecolors()[:, -1], alpha_flat)
assert_array_equal(coll2.get_facecolors()[:, -1], alpha_flat)
assert_array_equal(coll1.get_facecolors()[..., -1], alpha)
assert_array_equal(coll2.get_facecolors()[..., -1], alpha)


def test_alpha_validation():
Expand Down Expand Up @@ -992,7 +992,7 @@ def test_color_logic(pcfunc):
pc.update_scalarmappable() # This is called in draw().
# Define 2 reference "colors" here for multiple use.
face_default = mcolors.to_rgba_array(pc._get_default_facecolor())
mapped = pc.get_cmap()(pc.norm(z.ravel()))
mapped = pc.get_cmap()(pc.norm(z.ravel() if pcfunc == plt.pcolor else z))
# GitHub issue #1302:
assert mcolors.same_color(pc.get_edgecolor(), 'red')
# Check setting attributes after initialization:
Expand All @@ -1011,30 +1011,30 @@ def test_color_logic(pcfunc):
# Reset edgecolor to default.
pc.set_edgecolor(None)
pc.update_scalarmappable()
assert mcolors.same_color(pc.get_edgecolor(), mapped)
assert np.array_equal(pc.get_edgecolor(), mapped)
pc.set_facecolor(None) # restore default for facecolor
pc.update_scalarmappable()
assert mcolors.same_color(pc.get_facecolor(), mapped)
assert np.array_equal(pc.get_facecolor(), mapped)
assert mcolors.same_color(pc.get_edgecolor(), 'none')
# Turn off colormapping entirely:
pc.set_array(None)
pc.update_scalarmappable()
assert mcolors.same_color(pc.get_edgecolor(), 'none')
assert mcolors.same_color(pc.get_facecolor(), face_default) # not mapped
# Turn it back on by restoring the array (must be 1D!):
pc.set_array(z.ravel())
pc.set_array(z.ravel() if pcfunc == plt.pcolor else z)
Comment on lines 1024 to +1025
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Both of these situations feel undesirable...

  • The must be 1D! is the way it currently is and doesn't feel right after we've initialized our array with the 2D version pcolor(z).
  • It also doesn't feel great to change this and have to do the if pcfunc ... and change between 1D and 2D depending on which pcolor incantation I chose.

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The flattening in pcolormesh is a historical artifact; I think the move to accept it as fundamentally 2-D is good.
Pcolor is rarely a better choice than pcolormesh. When it is, it is likely because it can generate a set of
colored quadrilaterals that don't have to fill out a 2-D domain. I think we should embrace this difference between
pcolormesh and pcolor, so I don't have a problem with your special-casing in the test. I'm open to discussing
ideas for backwards-compatible improvements to pcolor, so that it could also take a 2-D array in set_array,
but it doesn't seem like a priority.

pc.update_scalarmappable()
assert mcolors.same_color(pc.get_facecolor(), mapped)
assert np.array_equal(pc.get_facecolor(), mapped)
assert mcolors.same_color(pc.get_edgecolor(), 'none')
# Give color via tuple rather than string.
pc = pcfunc(z, edgecolors=(1, 0, 0), facecolors=(0, 1, 0))
pc.update_scalarmappable()
assert mcolors.same_color(pc.get_facecolor(), mapped)
assert np.array_equal(pc.get_facecolor(), mapped)
assert mcolors.same_color(pc.get_edgecolor(), [[1, 0, 0, 1]])
# Provide an RGB array; mapping overrides it.
pc = pcfunc(z, edgecolors=(1, 0, 0), facecolors=np.ones((12, 3)))
pc.update_scalarmappable()
assert mcolors.same_color(pc.get_facecolor(), mapped)
assert np.array_equal(pc.get_facecolor(), mapped)
assert mcolors.same_color(pc.get_edgecolor(), [[1, 0, 0, 1]])
# Turn off the mapping.
pc.set_array(None)
Expand All @@ -1044,7 +1044,7 @@ def test_color_logic(pcfunc):
# And an RGBA array.
pc = pcfunc(z, edgecolors=(1, 0, 0), facecolors=np.ones((12, 4)))
pc.update_scalarmappable()
assert mcolors.same_color(pc.get_facecolor(), mapped)
assert np.array_equal(pc.get_facecolor(), mapped)
assert mcolors.same_color(pc.get_edgecolor(), [[1, 0, 0, 1]])
# Turn off the mapping.
pc.set_array(None)
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