Skip to content

Fix: Rounding error in get_data with tmin/tmax #13635

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
git-gigi wants to merge 6 commits into
base: main
Choose a base branch
from
Open

Fix: Rounding error in get_data with tmin/tmax #13635

Show file tree
Hide file tree
Changes from 4 commits
Commits
Show all changes
6 commits
Select commit Hold shift + click to select a range
2f91fdd
Fix: Rounding error in get_data with tmin/tmax (GH-13634)
git-gigi Feb 4, 2026
d459384
[pre-commit.ci] auto fixes from pre-commit.com hooks
pre-commit-ci[bot] Feb 4, 2026
3995e9b
Refactor: Move fix to BaseEpochs to fix Raw regression
git-gigi Feb 4, 2026
a7746ad
[pre-commit.ci] auto fixes from pre-commit.com hooks
pre-commit-ci[bot] Feb 4, 2026
fbb02fe
Style: Remove Italian comment
git-gigi Feb 4, 2026
6831f80
[pre-commit.ci] auto fixes from pre-commit.com hooks
pre-commit-ci[bot] Feb 4, 2026
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
29 changes: 29 additions & 0 deletions mne/epochs.py
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -1595,6 +1595,35 @@ def _handle_empty(self, on_empty, meth):
)
_on_missing(on_empty, msg, error_klass=RuntimeError)

def _handle_tmin_tmax(self, tmin, tmax):
Copy link
Member

@drammock drammock Feb 4, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

adding a new private method to Epochs that has the same name as an existing utility function is not the right way to go about this. It duplicates code and introduces the possibility of epochs behaving differently than Raw/Evoked for example.

Copy link
Author

@git-gigi git-gigi Feb 4, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Thanks for the review @drammock.

I understand the concern about code duplication. I initially tried modifying the shared _handle_tmin_tmax in mixin.py, but adding use_rounding=True there caused regressions in Raw tests (shifting data by one sample on Windows environments due to float precision). That's why I attempted the override in Epochs.

The core issue linked (#13634) is that epochs.crop(tmin=t) includes a sample that epochs.get_data(tmin=t) excludes. Since crop uses rounding internally, users expect get_data to match that behavior for consistency.

If modifying the global mixin.py is risky for Raw backward compatibility, and overriding in Epochs is discouraged, do you have a suggestion on how to reconcile get_data with crop for Epochs specifically? Maybe passing a round_tmin argument to get_data?

Copy link
Member

@drammock drammock Feb 4, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

The core issue linked (#13634) is that epochs.crop(tmin=t) includes a sample that epochs.get_data(tmin=t) excludes. Since crop uses rounding internally, users expect get_data to match that behavior for consistency.

yes, that was clear from the issue description.

If modifying the global mixin.py is risky for Raw backward compatibility, and overriding in Epochs is discouraged, do you have a suggestion on how to reconcile get_data with crop for Epochs specifically? Maybe passing a round_tmin argument to get_data?

I suspect that the problem is not limited to Epochs, but also affects Raw and Evoked (and TFR... anything that inherits the mixin). I don't have a suggestion off the top of my head; as I said before, this will need some discussion. Changing how get_data() works (to accord with crop()) --- or vice-versa --- has potentially wide-reaching consequences. I know it's a single sample, but as you've seen it's enough to break our tests, and it's also enough to change the results of user's existing analysis code, or even cause that code to crash if re-run. We don't take that lightly.

"""Convert seconds to index into data."""
_validate_type(
tmin,
types=("numeric", None),
item_name="tmin",
type_name="int, float, None",
)
_validate_type(
tmax,
types=("numeric", None),
item_name="tmax",
type_name="int, float, None",
)

# handle tmin/tmax as start and stop indices into data array
n_times = self.times.size
# QUI c'è la fix specifica per le Epochs
Copy link
Member

@drammock drammock Feb 4, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

code comments in English please. But also: code comments should be more specific/useful than "here is the fix for Epochs". This one isn't really needed at all IMO

Suggested change
# QUI c'è la fix specifica per le Epochs

Copy link
Author

@git-gigi git-gigi Feb 4, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Sorry about that! I left a debug comment by mistake. I will remove it in the next commit

start = 0 if tmin is None else self.time_as_index(tmin, use_rounding=True)[0]
stop = (
n_times if tmax is None else self.time_as_index(tmax, use_rounding=True)[0]
)
Copy link
Member

@drammock drammock Feb 4, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

This will need some discussion. When use_rounding was introduced, it was determined that we shouldn't change the default:

#2311 (comment)


# truncate start/stop to the open interval [0, n_times]
start = min(max(0, start), n_times)
stop = min(max(0, stop), n_times)

return start, stop

@verbose
def _get_data(
self,
Expand Down
34 changes: 34 additions & 0 deletions mne/tests/test_epochs.py
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -4855,6 +4855,40 @@ def fun(data):
assert_array_equal(out.get_data(non_picks), epochs.get_data(non_picks))


def test_get_data_rounding():
"""Test that get_data respects rounding for tmin/tmax (gh-13634)."""
# Data setup mirroring the issue report
data = np.linspace(-3.5, 1, 451).reshape((1, 1, 451))
info = create_info(["test"], 100.0, "eeg")
epochs = EpochsArray(data, info, tmin=-3.5, verbose=False)

t = 0.77

# compare crop() vs get_data()
# crop() uses proper rounding internally, get_data() should match it.
val_crop = epochs.copy().crop(tmin=t).get_data()[0, 0, 0]
val_get_data = epochs.get_data(tmin=t)[0, 0, 0]

assert_allclose(
val_get_data,
val_crop,
atol=1e-12,
err_msg="get_data(tmin) does not match crop(tmin)",
)

# verification on time consistency
# ensure we are getting the sample corresponding exactly to time 't'
idx = np.where(epochs.times == t)[0][0]
val_direct = epochs.get_data()[0, 0, idx]

assert_allclose(
val_get_data,
val_direct,
atol=1e-12,
err_msg="get_data(tmin) does not match direct indexing",
)


def test_apply_function_epo_ch_access():
"""Test ch-access within apply function to epoch objects."""

Expand Down
Loading