update preload to support new single .set EEGLAB format

mne/io/eeglab/_eeglab.py

@@ -9,7 +9,7 @@
 except ImportError:  # scipy < 1.8
     from scipy.io.matlab.mio5 import MatlabFunction
     from scipy.io.matlab.mio5_params import MatlabOpaque
-from scipy.io import loadmat
+from scipy.io import loadmat, whosmat
 
 from ...utils import _import_pymatreader_funcs
 
@@ -71,13 +71,29 @@ def _check_for_scipy_mat_struct(data):  # taken from pymatreader.utils
     return data
 
 
-def _readmat(fname, uint16_codec=None):
+def _readmat(fname, uint16_codec=None, preload=False):
     try:
         read_mat = _import_pymatreader_funcs("EEGLAB I/O")
     except RuntimeError:  # pymatreader not installed
-        eeg = loadmat(
-            fname, squeeze_me=True, mat_dtype=False, uint16_codec=uint16_codec
-        )
+        if preload:
+            eeg = loadmat(
+                fname, squeeze_me=True, mat_dtype=False, uint16_codec=uint16_codec
+            )
+        else:
+            info_fields = ['setname', 'filename', 'filepath', 'subject', 'group', 'condition', 'session', 'comments', 'nbchan', 'trials', 'pnts', 'srate', 'xmin', 'xmax', 'times', 'icaact', 'icawinv', 'icasphere', 'icaweights', 'icachansind', 'chanlocs', 'urchanlocs', 'chaninfo', 'ref', 'event', 'urevent', 'eventdescription', 'epoch', 'epochdescription', 'reject', 'stats', 'specdata', 'specicaact', 'splinefile', 'icasplinefile', 'dipfit', 'history', 'saved', 'etc']
+            eeg = loadmat(
+                fname, variable_names=info_fields, squeeze_me=True, mat_dtype=False, uint16_codec=uint16_codec
+            )
+            variables = whosmat(str(fname))
+            for var in variables:
+                if var[0] == 'data':
+                    numeric_types = ['int8', 'int16', 'int32', 'int64', 'uint8', 'uint16', 'uint32', 'uint64', 'single', 'double']
+                    if var[2] in numeric_types:
+                        # in preload=False mode and data is in .set file
+                        eeg['data'] = str(fname)
+                    else:
+                        eeg['data'] = loadmat(fname, variable_names=['data'], squeeze_me=True, mat_dtype=False, uint16_codec=uint16_codec)
+                    break
         return _check_for_scipy_mat_struct(eeg)
     else:
         return read_mat(fname, uint16_codec=uint16_codec)

mne/io/eeglab/eeglab.py

@@ -39,17 +39,20 @@
 def _check_eeglab_fname(fname, dataname):
     """Check whether the filename is valid.
 
-    Check if the file extension is ``.fdt`` (older ``.dat`` being invalid) or
-    whether the ``EEG.data`` filename exists. If ``EEG.data`` file is absent
-    the set file name with .set changed to .fdt is checked.
+    Check if the file extension is ``.fdt`` (older ``.dat`` being invalid) 
+    or ``.set`` (new EEGLAB format) or whether the ``EEG.data`` filename exists. 
+    If ``EEG.data`` file is absent the set file name with .set changed to .fdt is checked.
     """
     fmt = str(op.splitext(dataname)[-1])
     if fmt == ".dat":
         raise NotImplementedError(
             "Old data format .dat detected. Please update your EEGLAB "
             "version and resave the data in .fdt format"
         )
-
+    if fmt != ".set" and fmt != ".fdt":
+        raise ValueError(
+            "The file extension must be .set or .fdt, not {}".format(fmt)
+        )
     basedir = op.dirname(fname)
     data_fname = op.join(basedir, dataname)
     if not op.exists(data_fname):
@@ -68,10 +71,10 @@ def _check_eeglab_fname(fname, dataname):
     return data_fname
 
 
-def _check_load_mat(fname, uint16_codec):
+def _check_load_mat(fname, uint16_codec, preload=False):
     """Check if the mat struct contains 'EEG'."""
     fname = _check_fname(fname, "read", True)
-    eeg = _readmat(fname, uint16_codec=uint16_codec)
+    eeg = _readmat(fname, uint16_codec=uint16_codec, preload=preload)
     if "ALLEEG" in eeg:
         raise NotImplementedError(
             "Loading an ALLEEG array is not supported. Please contact"
@@ -302,8 +305,6 @@ def read_raw_eeglab(
         If 'auto', the channel names containing ``EOG`` or ``EYE`` are used.
         Defaults to empty tuple.
     %(preload)s
-        Note that ``preload=False`` will be effective only if the data is
-        stored in a separate binary file.
     %(uint16_codec)s
     %(montage_units)s
 
@@ -420,8 +421,6 @@ class RawEEGLAB(BaseRaw):
         If 'auto', the channel names containing ``EOG`` or ``EYE`` are used.
         Defaults to empty tuple.
     %(preload)s
-        Note that preload=False will be effective only if the data is stored
-        in a separate binary file.
     %(uint16_codec)s
     %(montage_units)s
     %(verbose)s
@@ -447,7 +446,7 @@ def __init__(
         verbose=None,
     ):
         input_fname = str(_check_fname(input_fname, "read", True, "input_fname"))
-        eeg = _check_load_mat(input_fname, uint16_codec)
+        eeg = _check_load_mat(input_fname, uint16_codec, preload)
         if eeg.trials != 1:
             raise TypeError(
                 f"The number of trials is {eeg.trials:d}. It must be 1 for raw"
@@ -472,14 +471,6 @@ def __init__(
                 verbose=verbose,
             )
         else:
-            if preload is False or isinstance(preload, str):
-                warn(
-                    "Data will be preloaded. preload=False or a string "
-                    "preload is not supported when the data is stored in "
-                    "the .set file"
-                )
-            # can't be done in standard way with preload=True because of
-            # different reading path (.set file)
             if eeg.nbchan == 1 and len(eeg.data.shape) == 1:
                 n_chan, n_times = [1, eeg.data.shape[0]]
             else: