MAG L1D index error fix

[maxinelasp]

Change Summary

Addresses #2832. Just adds a check in the chunk generation to see if it's empty before continuing. I think the chunk can very rarely be empty in some cases if the spin inputs aren't what we expected. If the chunk is empty, it should be fine to skip past it and continue on. We already skip past chunks with too many NaNs, so it's an expected use case.

Overview

Just added a simple if and continue flow if the expected epoch list is empty.

File changes

[Copilot]

Pull request overview

Fixes a rare IndexError in MAG L1D spin-offset computation by skipping over chunk windows that unexpectedly contain no epochs, preventing downstream indexing into an empty chunk_epoch.

Changes:

• Add an empty-chunk guard in calculate_spin_offsets() to skip processing when chunk_epoch is empty.
• Emit a warning when an empty chunk is encountered to aid debugging/traceability.

Comments suppressed due to low confidence (1)

imap_processing/mag/l1d/mag_l1d_data.py:542

• np.nanmean is computed before the validity checks; when a chunk is all-NaN this still triggers RuntimeWarnings ("Mean of empty slice") even though the values are later discarded/replaced. Consider moving the nanmean calls to after the valid-count/size checks (or guarding them) to avoid noisy warnings and unnecessary work.

            # Check if more than half of the chunk data is NaN before processing
            x_valid_count: int = int(np.sum(~np.isnan(chunk_vectors[:, 0])))
            y_valid_count: int = int(np.sum(~np.isnan(chunk_vectors[:, 1])))
            total_points = len(chunk_vectors)

            # average the x and y axes (z is fixed, as the spin axis)
            avg_x = np.nanmean(chunk_vectors[:, 0])
            avg_y = np.nanmean(chunk_vectors[:, 1])

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