8000 Backport PR #14241 on branch v3.1.x (Fix linear segmented colormap with one element) by meeseeksmachine · Pull Request #14251 · matplotlib/matplotlib · GitHub
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Backport PR #14241 on branch v3.1.x (Fix linear segmented colormap with one element) #14251

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Merged
merged 1 commit into from
May 18, 2019
Merged

Backport PR #14241 on branch v3.1.x (Fix linear segmented colormap with one element) #14251

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24 changes: 14 additions & 10 deletions lib/matplotlib/colors.py
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Original file line number Diff line number Diff line change
Expand Up @@ -377,16 +377,20 @@ def makeMappingArray(N, data, gamma=1.0):
if (np.diff(x) < 0).any():
raise ValueError("data mapping points must have x in increasing order")
# begin generation of lookup table
x = x * (N - 1)
xind = (N - 1) * np.linspace(0, 1, N) ** gamma
ind = np.searchsorted(x, xind)[1:-1]

distance = (xind[1:-1] - x[ind - 1]) / (x[ind] - x[ind - 1])
lut = np.concatenate([
[y1[0]],
distance * (y0[ind] - y1[ind - 1]) + y1[ind - 1],
[y0[-1]],
])
if N == 1:
# convention: use the y = f(x=1) value for a 1-element lookup table
lut = np.array(y0[-1])
else:
x = x * (N - 1)
xind = (N - 1) * np.linspace(0, 1, N) ** gamma
ind = np.searchsorted(x, xind)[1:-1]

distance = (xind[1:-1] - x[ind - 1]) / (x[ind] - x[ind - 1])
lut = np.concatenate([
[y1[0]],
distance * (y0[ind] - y1[ind - 1]) + y1[ind - 1],
[y0[-1]],
])
# ensure that the lut is confined to values between 0 and 1 by clipping it
return np.clip(lut, 0.0, 1.0)

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10 changes: 10 additions & 0 deletions lib/matplotlib/tests/test_colors.py
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Original file line number Diff line number Diff line change
Expand Up @@ -16,6 +16,16 @@
from matplotlib.testing.decorators import image_comparison


@pytest.mark.parametrize('N, result', [
(5, [1, .6, .2, .1, 0]),
(2, [1, 0]),
(1, [0]),
])
def test_makeMappingArray(N, result):
data = [(0.0, 1.0, 1.0), (0.5, 0.2, 0.2), (1.0, 0.0, 0.0)]
assert_array_almost_equal(mcolors.makeMappingArray(N, data), result)


def test_resample():
"""
Github issue #6025 pointed to incorrect ListedColormap._resample;
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0