mne.channels.combine_channels(epochs) drops metadata

[cbrnr]

I think mne.channels.combine_channels(epochs) drops metadata (i.e. there is no epochs.metadata attribute in the resulting Epochs objects). I wanted to make sure that this is not intended – if it is a bug I'm happy to submit a PR.

[cbrnr]

Reprex:

import mne

root = mne.datasets.sample.data_path() / 'MEG' / 'sample'
raw = mne.io.read_raw_fif(root / 'sample_audvis_filt-0-40_raw.fif', preload=False)
events = mne.read_events(root / 'sample_audvis_filt-0-40_raw-eve.fif')
raw.crop(tmax=90)
raw.pick(['eeg', 'eog']).load_data()
raw.rename_channels({name: name.replace(' 0', '').lower() for name in raw.ch_names})

event_dict = {
    'auditory/left': 1,
    'auditory/right': 2,
    'visual/left': 3,
    'visual/right': 4,
    'face': 5,
    'buttonpress': 32
}

metadata, events, event_id = mne.epochs.make_metadata(
    events=events,
    event_id=event_dict,
    tmin=-0.3,
    tmax=0.7,
    sfreq=raw.info['sfreq']
)

epochs = mne.Epochs(
    raw,
    events,
    event_id=event_dict,
    tmin=-0.3,
    tmax=0.7,
    metadata=metadata,
    preload=True
)

print(epochs.metadata)  # metadata is still there
print(
    mne.channels.combine_channels(
        epochs,
        {"ROI1": mne.pick_channels(epochs.ch_names, include=["eeg01", "eeg02", "eeg03"])}
    ).metadata  # metadata is gone
)