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Fix ZeroDivisionError in LinearColormap.to_step() with a single step #227

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Fix ZeroDivisionError in LinearColormap.to_step() with a single step #227

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20 changes: 14 additions & 6 deletions branca/colormap.py
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Original file line number Diff line number Diff line change
Expand Up @@ -445,12 +445,20 @@ def to_step(
if round_method == "log10":
index = [_base(x) for x in index]

colors = [
scaled_cm.rgba_floats_tuple(
index[i] * (1.0 - i / (n - 1.0)) + index[i + 1] * i / (n - 1.0),
)
for i in range(n)
]
if n == 1:
# Steps are normally sampled at points spread evenly across the
# colormap, the first at `index[0]` and the last at `index[-1]`.
# A single step is the degenerate case of that spread (0 / 0), so
# sample the middle instead: the one bin covers the whole range
# and gets a color to match.
colors = [scaled_cm.rgba_floats_tuple((index[0] + index[1]) / 2.0)]
else:
colors = [
scaled_cm.rgba_floats_tuple(
index[i] * (1.0 - i / (n - 1.0)) + index[i + 1] * i / (n - 1.0),
)
for i in range(n)
]

caption = self.caption
text_color = self.text_color
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19 changes: 19 additions & 0 deletions tests/test_colormap.py
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Original file line number Diff line number Diff line change
Expand Up @@ -89,6 +89,25 @@ def test_linear_to_step():
lc.to_step(data=some_list, quantiles=[0, 0.3, 0.7, 1], round_method="log10")


@pytest.mark.parametrize(
"kwargs",
[
{"n": 1},
{"index": [0, 1]},
{"data": [0, 0.5, 1], "n": 1},
{"data": [0.5, 0.75, 1], "n": 1, "method": "log"},
{"data": [0, 0.5, 1], "quantiles": [0, 1]},
],
)
def test_linear_to_step_single_step(kwargs):
"""A one-bin colormap is valid; every path here raised ZeroDivisionError."""
linear = cm.LinearColormap(["red", "blue"], vmin=0, vmax=1)
step = linear.to_step(**kwargs)
assert len(step.colors) == 1
# The single bin spans the whole range, so it takes the middle color.
assert step.colors[0] == linear.rgba_floats_tuple(0.5)


def test_step_to_linear():
step = cm.StepColormap(
["green", "yellow", "red"],
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