MRG, BUG: Make sure resample return at least one sample (mne-tools#9897)

* TST: Expose failure when resampling to 1 sample with sfreq > len(times) [ci skip]

* raise a RuntimeError when resampling yields 0 datapoints.

* Change raised error to match numpy error raised in numpy/fft/_pocketfft:94: in _get_backward_norm

* fix regex match pattern.

* return 1 sample instead of raising.

* FIX: One more max

* Add entry to latest.inc.

* DOC: Add name

* DOC: Update [ci skip]

Co-authored-by: Eric Larson <[email protected]>

doc/changes/latest.inc

@@ -231,6 +231,8 @@ Bugs
 
 - Fix bug where :func:`mne.time_frequency.psd_array_welch` and :func:`mne.time_frequency.psd_array_multitaper` failed to handle negative integer for ``n_jobs`` argument (:gh:`9849` **by new contributor** |Riessarius Stargardsky|_)
 
+- Fix bug where resampling returns empty instances (:gh:`9897` **by new contributor** |Mathieu Scheltienne|_ and `Eric Larson`_)
+
 - Fix bug with :func:`mne.io.read_raw_nihon` where latin-1 annotations could not be read (:gh:`9384` by `Alex Gramfort`_)
 
 - Fix bug when printing a :class:`mne.io.RawArray` in the notebook (:gh:`9404` by `Alex Gramfort`_)
@@ -347,4 +349,4 @@ API changes
 
 - Deprecate ``mne.viz.utils.center_cmap`` (:gh:`9851` by `Clemens Brunner`_)
 
-- Add depreciation warning for the default partial pathlength factor of :func:`mne.preprocessing.nirs.beer_lambert_law` from 0.1 to 6 (:gh:`9843` by `Robert Luke`_)
+- The default partial pathlength factor of :func:`mne.preprocessing.nirs.beer_lambert_law` will change from 0.1 in 0.24 to 6.0 in the next release (:gh:`9843` by `Robert Luke`_)

mne/filter.py

@@ -1380,7 +1380,7 @@ def _check_filterable(x, kind='filtered'):
 
 def _resamp_ratio_len(up, down, n):
     ratio = float(up) / down
-    return ratio, int(round(ratio * n))
+    return ratio, max(int(round(ratio * n)), 1)
 
 
 @verbose
@@ -1469,7 +1469,7 @@ def resample(x, up=1., down=1., npad=100, axis=-1, window='boxcar', n_jobs=1,
     # prep for resampling now
     x_flat = x.reshape((-1, x_len))
     orig_len = x_len + npads.sum()  # length after padding
-    new_len = int(round(ratio * orig_len))  # length after resampling
+    new_len = max(int(round(ratio * orig_len)), 1)  # length after resampling
     to_removes = [int(round(ratio * npads[0]))]
     to_removes.append(new_len - final_len - to_removes[0])
     to_removes = np.array(to_removes)

mne/tests/test_filter.py

@@ -7,7 +7,7 @@
 import pytest
 from scipy.signal import resample as sp_resample, butter, freqz, sosfreqz
 
-from mne import create_info
+from mne import create_info, Epochs
 from numpy.fft import fft, fftfreq
 from mne.io import RawArray, read_raw_fif
 from mne.io.pick import _DATA_CH_TYPES_SPLIT
@@ -327,6 +327,31 @@ def test_resample_raw():
     assert data.shape == (1, 63)
 
 
+def test_resample_below_1_sample():
+    """Test resampling doesn't yield datapoints."""
+    # Raw
+    x = np.zeros((1, 100))
+    sfreq = 1000.
+    raw = RawArray(x, create_info(1, sfreq, 'eeg'))
+    raw.resample(5)
+    assert len(raw.times) == 1
+    assert raw.get_data().shape[1] == 1
+
+    # Epochs
+    x = np.zeros((1, 10000))
+    sfreq = 1000.
+    raw = RawArray(x, create_info(1, sfreq, 'eeg'))
+    events = np.array([[400, 0, 1],
+                      [2000, 0, 1],
+                      [3000, 0, 1]])
+    epochs = Epochs(raw, events, {'test': 1}, 0, 0.2, proj=False,
+                    picks='eeg', baseline=None, preload=True,
+                    verbose=False)
+    epochs.resample(1)
+    assert len(epochs.times) == 1
+    assert epochs.get_data().shape[2] == 1
+
+
 @pytest.mark.slowtest
 def test_filters():
     """Test low-, band-, high-pass, and band-stop filters plus resampling."""