BUG: Compensation channels pick error

While trying to execute evoked.interpolate_bads(), I ran into the following error:

  mne\channels\interpolation.py", line 190, in _interpolate_bads_meg
    info_to = pick_info(inst.info, picks_bad)

  mne\io\pick.py", line 411, in pick_info
    'channels' % (current_comp, comps_missing))

RuntimeError: Compensation grade 3 has been applied, but compensation channels are missing: ['BG1-2805', 'BG2-2805', 'BG3-2805', 'G11-2805', 'G12-2805', 'G13-2805', 'G22-2805', 'G23-2805', 'P11-2805', 'P13-2805', 'Q11-2805', 'Q13-2805', 'R11-2805', 'R12-2805', 'R13-2805', 'R22-2805', 'R23-2805']
Either remove compensation or pick compensation channels

This error seems to be raised automatically when attempting to make any pick that does not include all ref_meg channels. I dug a bit into compensation grades, and it seems that it can only be removed for Raw data using the apply_gradient_compensation(0) method.

Maybe it would be better to turn this error into a warning? Indeed in my case, compensation channels are not removed from data, the function only attempts to separately pick bad channels to compute interpolation. Another way could be to always include these channels, similar to the ref_meg='auto' argument of pick_types(), but I’m not sure it would make sense in every case (especially this one). Thanks,

[agramfort]

you will need to wait for the next release or switch to using the current development version.

See https://github.com/mne-tools/mne-python#get-the-latest-code

[larsoner]

I think you meant to link here

https://gist.github.com/Heneark/a183a24218302831860efc86c84c1950

Thanks for making it. We want to fix the problem generally, but the best solution will take some time. In the meantime it’s quicker to squash the bugs one by one.