Fix changes in SSD for backward compatibility

examples/decoding/ssd_spatial_filters.py

@@ -13,6 +13,7 @@
 frequency band of interest and the noise covariance based on surrounding
 frequencies.
 """
+
 # Author: Denis A. Engemann <denis.engemann@gmail.com>
 #         Victoria Peterson <victoriapeterson09@gmail.com>
 # License: BSD-3-Clause
@@ -82,8 +83,8 @@
     ssd_sources, sfreq=raw.info["sfreq"], n_fft=4096
 )
 
-# Get spec_ratio information (already sorted).
-# Note that this is not necessary if sort_by_spectral_ratio=True (default).
+# Get spec_ratio information (already sorted)
+# Note that this is not necessary if sort_by_spectral_ratio=True (default)
 spec_ratio, sorter = ssd.get_spectral_ratio(ssd_sources)
 
 # Plot spectral ratio (see Eq. 24 in Nikulin et al., 2011).

mne/decoding/ssd.py

@@ -289,6 +289,39 @@ def fit_transform(self, X, y=None, **fit_params):
         # use parent TransformerMixin method but with custom docstring
         return super().fit_transform(X, y=y, **fit_params)
 
+    def get_spectral_ratio(self, ssd_sources):
+        """Get the spectal signal-to-noise ratio for each spatial filter.
+
+        Spectral ratio measure for best n_components selection
+        See :footcite:`NikulinEtAl2011`, Eq. (24).
+
+        Parameters
+        ----------
+        ssd_sources : array
+            Data projected to SSD space.
+
+        Returns
+        -------
+        spec_ratio : array, shape (n_channels)
+            Array with the sprectal ratio value for each component.
+        sorter_spec : array, shape (n_channels)
+            Array of indices for sorting spec_ratio.
+
+        References
+        ----------
+        .. footbibliography::
+        """
+        from ._mod_ged import _get_spectral_ratio
+
+        spec_ratio, sorter_spec = _get_spectral_ratio(
+            ssd_sources=ssd_sources,
+            sfreq=self.sfreq_,
+            n_fft=self.n_fft_,
+            freqs_signal=self.freqs_signal_,
+            freqs_noise=self.freqs_noise_,
+        )
+        return spec_ratio, sorter_spec
+
     def inverse_transform(self):
         """Not implemented yet."""
         raise NotImplementedError("inverse_transform is not yet available.")

mne/decoding/tests/test_ssd.py

@@ -570,6 +570,44 @@ def test_picks_arg():
     ssd.fit(X).transform(X)
 
 
+def test_get_spectral_ratio():
+    """Test that method is the same as function in _mod_ged.py."""
+    X, _, _ = simulate_data()
+    sf = 250
+    n_channels = X.shape[0]
+    info = create_info(ch_names=n_channels, sfreq=sf, ch_types="eeg")
+
+    # Init
+    filt_params_signal = dict(
+        l_freq=freqs_sig[0],
+        h_freq=freqs_sig[1],
+        l_trans_bandwidth=1,
+        h_trans_bandwidth=1,
+    )
+    filt_params_noise = dict(
+        l_freq=freqs_noise[0],
+        h_freq=freqs_noise[1],
+        l_trans_bandwidth=1,
+        h_trans_bandwidth=1,
+    )
+
+    ssd = SSD(
+        info,
+        filt_params_signal,
+        filt_params_noise,
+        n_components=None,
+        sort_by_spectral_ratio=False,
+    )
+    ssd.fit(X)
+    ssd_sources = ssd.transform(X)
+    spec_ratio_ssd, sorter_spec_ssd = ssd.get_spectral_ratio(ssd_sources)
+    spec_ratio_ged, sorter_spec_ged = _get_spectral_ratio(
+        ssd_sources, ssd.sfreq_, ssd.n_fft_, ssd.freqs_signal_, ssd.freqs_noise_
+    )
+    assert_array_equal(spec_ratio_ssd, spec_ratio_ged)
+    assert_array_equal(sorter_spec_ssd, sorter_spec_ged)
+
+
 @pytest.mark.filterwarnings("ignore:.*invalid value encountered in divide.*")
 @pytest.mark.filterwarnings("ignore:.*is longer than.*")
 @parametrize_with_checks(