fix(graph): spread the subsample slices over the whole series

glances/globals.py

@@ -181,8 +181,9 @@ def subsample(data, sampling):
     """
     if len(data) <= sampling:
         return data
-    sampling_length = int(round(len(data) / float(sampling)))
-    return [mean(data[s * sampling_length : (s + 1) * sampling_length]) for s in range(0, sampling)]
+    # Slice bounds spread over the whole list: no slice is empty, none is left out
+    bounds = [s * len(data) // sampling for s in range(sampling + 1)]
+    return [mean(data[bounds[s] : bounds[s + 1]]) for s in range(0, sampling)]
 
 
 def time_series_subsample(data, sampling):
@@ -196,9 +197,9 @@ def time_series_subsample(data, sampling):
         return data
     t = [t[0] for t in data]
     v = [t[1] for t in data]
-    sampling_length = int(round(len(data) / float(sampling)))
-    t_subsampled = [t[s * sampling_length : (s + 1) * sampling_length][0] for s in range(0, sampling)]
-    v_subsampled = [mean(v[s * sampling_length : (s + 1) * sampling_length]) for s in range(0, sampling)]
+    bounds = [s * len(data) // sampling for s in range(sampling + 1)]
+    t_subsampled = [t[bounds[s]] for s in range(0, sampling)]
+    v_subsampled = [mean(v[bounds[s] : bounds[s + 1]]) for s in range(0, sampling)]
     return list(zip(t_subsampled, v_subsampled))
 
 

tests/test_core.py

@@ -22,7 +22,14 @@
     UTC = timezone.utc
 
 from glances.filter import GlancesFilter, GlancesFilterList
-from glances.globals import auto_unit, pretty_date, split_esc, string_value_to_float, subsample
+from glances.globals import (
+    auto_unit,
+    pretty_date,
+    split_esc,
+    string_value_to_float,
+    subsample,
+    time_series_subsample,
+)
 from glances.outputs.glances_bars import Bar
 
 
@@ -42,6 +49,21 @@ def test_016_subsample(self):
         ]:
             l_subsample = subsample(l_test[0], l_test[1])
             self.assertLessEqual(len(l_subsample), l_test[1])
+        # 1200 values in 800 points (graph export defaults): no empty slice
+        self.assertEqual(len(subsample(list(range(1200)), 800)), 800)
+        # 1000 values in 800 points: the last values are kept (mean of 998 and 999)
+        self.assertEqual(subsample(list(range(1000)), 800)[-1], 998.5)
+
+    def test_017_time_series_subsample(self):
+        """Test time series subsampling function."""
+        print('INFO: [TEST_017] Time series subsampling')
+        for length, sampling in [(3, 4), (8, 4), (15, 10), (1000, 800), (1200, 800), (8000, 800)]:
+            data = [(t, float(t)) for t in range(length)]
+            l_subsample = time_series_subsample(data, sampling)
+            self.assertEqual(len(l_subsample), min(length, sampling))
+            # The first point starts the series, the last points end it
+            self.assertEqual(l_subsample[0][0], 0)
+            self.assertGreater(l_subsample[-1][1], length - 1 - length / sampling)
 
     def test_018_string_value_to_float(self):
         """Check string_value_to_float function"""