Epochs.apply_function(channel_wise=False, picks=…) silently ignores picks

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While documenting the shape passed to fun for Epochs.apply_function (#13118), I noticed a behavioral asymmetry between Raw and Epochs that doesn’t appear to be documented anywhere.

When channel_wise=False:

  • For Raw, picks is applied.
  • For Epochs, picks is silently ignored.

Example

import numpy as np, mne
data = np.random.randn(3, 4, 50)
info = mne.create_info(["ch0","ch1","ch2","ch3"], sfreq=100., ch_types="eeg")
epochs = mne.EpochsArray(data, info, verbose=False)
raw    = mne.io.RawArray(np.random.randn(4, 150), info, verbose=False)

shapes = []
def spy(x):
    shapes.append(x.shape); return x

epochs.copy().apply_function(spy, channel_wise=False, picks=["ch0"])
print("Epochs:", shapes)   # [(3, 4, 50)]  -> picks ignored
shapes.clear()                                                                                                     

raw.copy().apply_function(spy, channel_wise=False, picks=["ch0"])
print("Raw:   ", shapes)   # [(1, 150)]    -> picks applied