Add metadata to combine_channels (#10504)

* Add metadata to combine_channels

* Update mne/channels/channels.py

Co-authored-by: Alexandre Gramfort <[email protected]>

* Add changelog entry

* Add test

Co-authored-by: Alexandre Gramfort <[email protected]>

Author: cbrnr

doc/changes/latest.inc

@@ -35,6 +35,8 @@ Bugs
 
 - Fix behavior for the ``pyvista`` 3D renderer's ``quiver3D`` function so that default arguments plot a glyph in ``arrow`` mode (:gh:`10493` by `Alex Rockhill`_)
 
+- Retain epochs metadata when using :func:`mne.channels.combine_channels` (:gh:`10504` by `Clemens Brunner`_)
+
 API changes
 ~~~~~~~~~~~
 - None yet

mne/channels/channels.py

@@ -1710,6 +1710,8 @@ def combine_channels(inst, groups, method='mean', keep_stim=False,
     elif isinstance(inst, BaseEpochs):
         combined_inst = EpochsArray(new_data, info, events=inst.events,
                                     tmin=inst.times[0])
+        if inst.metadata is not None:
+            combined_inst.metadata = inst.metadata.copy()
     elif isinstance(inst, Evoked):
         combined_inst = EvokedArray(new_data, info, tmin=inst.times[0])
 

mne/channels/tests/test_channels.py

@@ -24,7 +24,7 @@
 from mne import (pick_types, pick_channels, EpochsArray, EvokedArray,
                  make_ad_hoc_cov, create_info, read_events, Epochs)
 from mne.datasets import testing
-from mne.utils import requires_version
+from mne.utils import requires_pandas, requires_version
 
 io_dir = op.join(op.dirname(__file__), '..', '..', 'io')
 base_dir = op.join(io_dir, 'tests', 'data')
@@ -520,3 +520,20 @@ def test_combine_channels():
         combine_channels(raw, warn2)
         combine_channels(raw_ch_bad, warn3, drop_bad=True)
     assert len(record) == 3
+
+
+@requires_pandas
+def test_combine_channels_metadata():
+    """Test if metadata is correctly retained in combined object."""
+    import pandas as pd
+
+    raw = read_raw_fif(raw_fname, preload=True)
+    epochs = Epochs(raw, read_events(eve_fname), preload=True)
+
+    metadata = pd.DataFrame({"A": np.arange(len(epochs)),
+                             "B": np.ones(len(epochs))})
+    epochs.metadata = metadata
+
+    good = dict(foo=[0, 1, 3, 4], bar=[5, 2])  # good grad and mag
+    combined_epochs = combine_channels(epochs, good)
+    pd.testing.assert_frame_equal(epochs.metadata, combined_epochs.metadata)