[FIX] naming parsing for bids files (mne-tools#5570)

this fixes the order of arguments in the filename construction for BIDS files. essentially, it looks to see if the filename string has the specific modality, it pops it off to infix the part argument then adds the modality as a suffix to the filename.

doc/manual/c_reference.rst

@@ -1479,7 +1479,7 @@ anatomy only, not on the MEG/EEG data to be analyzed.
 		R_{13} & R_{13} & R_{13} & z_0 \\
 		0 & 0 & 0 & 1
 		\end{bmatrix}
-	     
+
 defined so that if the augmented location vectors in MRI
 head and MRI coordinate systems are denoted by :math:`r_{head}[x_{head}\ y_{head}\ z_{head}\ 1]` and :math:`r_{MRI}[x_{MRI}\ y_{MRI}\ z_{MRI}\ 1]`,
 respectively,

mne/io/base.py

@@ -14,6 +14,7 @@
 import numpy as np
 
 from .constants import FIFF
+from .utils import _construct_bids_filename
 from .pick import pick_types, channel_type, pick_channels, pick_info
 from .pick import _pick_data_channels, _pick_data_or_ica
 from .meas_info import write_meas_info
@@ -2258,9 +2259,8 @@ def _write_raw(fname, raw, info, picks, fmt, data_type, reset_range, start,
         if split_naming == 'neuromag':
             # insert index in filename
             use_fname = '%s-%d%s' % (base, part_idx, ext)
-        else:
-            # insert index in filename
-            use_fname = '%s_part-%02d_meg%s' % (base, part_idx, ext)
+        elif split_naming == 'bids':
+            use_fname = _construct_bids_filename(base, ext, part_idx)
             # check for file existence
             _check_fname(use_fname, overwrite)
 

mne/io/fiff/tests/test_raw_fiff.py

@@ -398,24 +398,26 @@ def test_split_files():
     raw_crop = raw_1.copy().crop(0, 1.)
 
     assert_allclose(raw_1.buffer_size_sec, 10., atol=1e-2)  # samp rate
-    split_fname = op.join(tempdir, 'split_raw.fif')
+    split_fname = op.join(tempdir, 'split_raw_meg.fif')
     # intended filenames
-    split_fname_elekta_part2 = op.join(tempdir, 'split_raw-1.fif')
+    split_fname_elekta_part2 = op.join(tempdir, 'split_raw_meg-1.fif')
     split_fname_bids_part1 = op.join(tempdir, 'split_raw_part-01_meg.fif')
     split_fname_bids_part2 = op.join(tempdir, 'split_raw_part-02_meg.fif')
     raw_1.set_annotations(Annotations([2.], [5.5], 'test'))
-    raw_1.save(split_fname, buffer_size_sec=1.0, split_size='10MB')
+    with pytest.warns(RuntimeWarning, match='does not conform to MNE'):
+        raw_1.save(split_fname, buffer_size_sec=1.0, split_size='10MB')
 
     # check that the filenames match the intended pattern
     assert op.exists(split_fname_elekta_part2)
     # check that filenames are being formatted correctly for BIDS
-    raw_1.save(split_fname,
-               buffer_size_sec=1.0, split_size='10MB',
-               split_naming='bids',
-               overwrite=True)
+    with pytest.warns(RuntimeWarning, match='does not conform to MNE'):
+        raw_1.save(split_fname, buffer_size_sec=1.0, split_size='10MB',
+                   split_naming='bids', overwrite=True)
     assert op.exists(split_fname_bids_part1)
     assert op.exists(split_fname_bids_part2)
 
+    split_fname = op.join(tempdir, 'split_raw.fif')
+    raw_1.save(split_fname, buffer_size_sec=1.0, split_size='10MB')
     raw_2 = read_raw_fif(split_fname)
     assert_allclose(raw_2.buffer_size_sec, 1., atol=1e-2)  # samp rate
     assert_array_almost_equal(raw_1.annotations.onset, raw_2.annotations.onset)

mne/io/utils.py

@@ -249,3 +249,18 @@ def _synthesize_stim_channel(events, n_samples):
     for onset, duration, trigger in events:
         stim_channel[onset:onset + duration] = trigger
     return stim_channel
+
+
+def _construct_bids_filename(base, ext, part_idx):
+    """Construct a BIDS compatible filename for split files."""
+    # insert index in filename
+    deconstructed_base = base.split('_')
+    bids_supported = ['meg', 'eeg', 'ieeg']
+    for mod in bids_supported:
+        if mod in deconstructed_base:
+            idx = deconstructed_base.index(mod)
+            modality = deconstructed_base.pop(idx)
+    base = '_'.join(deconstructed_base)
+    use_fname = '%s_part-%02d_%s%s' % (base, part_idx, modality, ext)
+
+    return use_fname