[BUG] Drop annotations with NaN onset in EEGLAB raw files

doc/changes/devel/12484.bugfix.rst

@@ -0,0 +1 @@
+- Fix problem caused by onsets with NaN values using :func:`mne.io.read_raw_eeglab` by `Jacob Woessner`_

mne/io/eeglab/eeglab.py

@@ -799,6 +799,22 @@ def _read_annotations_eeglab(eeg, uint16_codec=None):
             )
             duration[idx] = np.nan if is_empty_array else event.duration
 
+    # Drop events with NaN onset see PR #12484
+    valid_indices = [
+        idx for idx, onset_idx in enumerate(onset) if not np.isnan(onset_idx)
+    ]
+    n_dropped = len(onset) - len(valid_indices)
+    if len(valid_indices) != len(onset):
+        warn(
+            f"{n_dropped} events have an onset that is NaN. These values are "
+            "usually ignored by EEGLAB and will be dropped from the "
+            "annotations."
+        )
+
+    onset = np.array([onset[idx] for idx in valid_indices])
+    duration = np.array([duration[idx] for idx in valid_indices])
+    description = [description[idx] for idx in valid_indices]
+
     return Annotations(
         onset=np.array(onset) / eeg.srate,
         duration=duration / eeg.srate,

mne/io/eeglab/tests/test_eeglab.py

@@ -719,3 +719,36 @@ def get_bad_information(eeg, get_pos, *, montage_units):
     assert len(pos["lpa"]) == 3
     assert len(pos["rpa"]) == 3
     assert len(raw.info["dig"]) == n_eeg + 3
+
+
+@testing.requires_testing_data
+def test_eeglab_drop_nan_annotations(tmp_path):
+    """Test reading file with NaN annotations."""
+    pytest.importorskip("eeglabio")
+    from eeglabio.raw import export_set
+
+    file_path = tmp_path / "test_nan_anno.set"
+    raw = read_raw_eeglab(raw_fname_mat, preload=True)
+    data = raw.get_data()
+    sfreq = raw.info["sfreq"]
+    ch_names = raw.ch_names
+    anno = [
+        raw.annotations.description,
+        raw.annotations.onset,
+        raw.annotations.duration,
+    ]
+    anno[1][0] = np.nan
+
+    export_set(
+        str(file_path),
+        data,
+        sfreq,
+        ch_names,
+        ch_locs=None,
+        annotations=anno,
+        ref_channels="common",
+        ch_types=np.repeat("EEG", len(ch_names)),
+    )
+
+    with pytest.raises(RuntimeWarning, match="1 .* have an onset that is NaN.*"):
+        raw = read_raw_eeglab(file_path, preload=True)