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fix: Allow image coordinate irregularity equal to the tolerance #6915

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hoxbro merged 3 commits into from
Jun 24, 2026
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fix: Allow image coordinate irregularity equal to the tolerance #6915

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789e434
Add tests of irregular date-time image coordinates
stanwest Jun 12, 2026
1321e24
Allow irregular sampling equal to the tolerance
stanwest Jun 12, 2026
ade0ed3
Clarify description of test
stanwest Jun 15, 2026
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2 changes: 1 addition & 1 deletion holoviews/core/util/__init__.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2255,7 +2255,7 @@ def validate_regular_sampling(values, rtol=10e-6):
if len(diffs) < 1:
return True
min_diff = diffs.min()
return abs(min_diff - diffs.max()) < abs(min_diff * rtol)
return abs(min_diff - diffs.max()) <= abs(min_diff * rtol)


def compute_density(start, end, length, time_unit="us"):
Expand Down
51 changes: 51 additions & 0 deletions holoviews/tests/element/test_image.py
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Expand Up @@ -4,6 +4,8 @@

from __future__ import annotations

import datetime as dt

import numpy as np
import pytest

Expand Down Expand Up @@ -74,6 +76,55 @@ def test_image_rtol_config(self):
hv.Image({"vals": vals, "xs": xs, "ys": ys}, ["xs", "ys"], "vals")
hv.config.image_rtol = image_rtol

@pytest.mark.parametrize(
"x",
[
# max(|step|) / min(|step|) - 1 = 0.0015
[dt.datetime(2017, 1, 1, 0, 0, 0, ms) for ms in [0, 10000, 20015]],
*(
np.array([0, 10000, 20015]).astype(f"datetime64[{unit}]")
for unit in ["D", "h", "m", "s", "ms", "us"]
),
],
)
def test_image_datetime_rtol_failure(self, x):
"""
Constructing an Image with a date-time coordinate warns about irregular sampling
if, approximately speaking, one less than the ratio of the max and min steps
exceeds the default `image_rtol`.
"""
Comment on lines +91 to +95

@hoxbro hoxbro Jun 13, 2026

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Suggested change
"""
Constructing an Image with a date-time coordinate warns about irregular sampling
if, approximately speaking, one less than the ratio of the max and min steps
exceeds the default `image_rtol`.
"""

Docstrings is not needed for tests.

@stanwest stanwest Jun 15, 2026

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I understand. I see the docstring as a natural place to explain the intent of a non-obvious test. Here, in particular, it relates the test to image_rtol, a relationship that isn't apparent from the test's parameters, which are declared independently of image_rtol. Would a comment be preferred over a docstring?

y = np.arange(2)
hv.Image((x, y, np.zeros((len(y), len(x)))))
self.log_handler.assert_endswith(
"WARNING",
"set a higher tolerance on hv.config.image_rtol or the rtol parameter in "
"the Image constructor.",
)

@pytest.mark.parametrize(
"x",
[
# |granularity / step| = 1/400 = 0.0025
[dt.datetime(2017, 1, 1, 0, 0, 0, ms) for ms in [0, 400]],
# |granularity / step| = 1/800 = 0.00125
Comment on lines +107 to +109

@hoxbro hoxbro Jun 13, 2026

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Why did you choose two different ratios?

@stanwest stanwest Jun 15, 2026

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Because datetime.timedelta and np.timedelta64 instances round differently when multiplied by a float such as image_rtol, the range of coordinate steps that will cause the false warning differs for the two types. (A datetime.timedelta instance rounds to the nearest microseconds, whereas a np.timedelta64 truncates toward zero.) Specifically, with image_rtol = 0.001, the false warning occurs for datetime.datetime steps of less than 500 microseconds and for np.datetime64 steps of less than 1000 units. For each type, I chose a step that is a little smaller than the largest sufficient step for that type.

*(
np.array([10000, 10800]).astype(f"datetime64[{unit}]")
for unit in ["D", "h", "m", "s", "ms", "us"]
),
],
)
def test_image_datetime_rtol_granularity(self, x):
"""
Constructing an Image with an evenly spaced date-time coordinate does not warn
about irregular sampling, even when the ratio of the date-time granularity to
the coordinate step is greater than the default `image_rtol` (or twice
`image_rtol` for `datetime.datetime` types because of how they round when
multiplied by a `float`).
"""
Comment on lines +117 to +123

@hoxbro hoxbro Jun 13, 2026

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Suggested change
"""
Constructing an Image with an evenly spaced date-time coordinate does not warn
about irregular sampling, even when the ratio of the date-time granularity to
the coordinate step is greater than the default `image_rtol` (or twice
`image_rtol` for `datetime.datetime` types because of how they round when
multiplied by a `float`).
"""

y = np.arange(2)
hv.Image((x, y, np.zeros((len(y), len(x)))))
assert len(self.log_handler.tail("WARNING", n=1)) == 0

def test_image_clone(self):
vals = np.random.rand(20, 20)
xs = np.linspace(0, 10, 20)
Expand Down
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