Merge pull request #541 from linsword13/cv-stats

Add coefficient of variance to summary stats

lib/ramble/ramble/test/util/stats.py

@@ -28,6 +28,14 @@
             "s",
             (4, "repeats", "summary::n_successful_repeats"),
         ),
+        (ramble.util.stats.StatsCoefficientOfVariation(), [3], "s", ("NA", "", "summary::cv")),
+        (ramble.util.stats.StatsCoefficientOfVariation(), [3, -3], "s", ("NA", "", "summary::cv")),
+        (
+            ramble.util.stats.StatsCoefficientOfVariation(),
+            [6.79, 5.6, 4.31, 5.5],
+            "s",
+            (0.18, "", "summary::cv"),
+        ),
     ],
 )
 def test_stats_for_repeat_foms(statistic, input_values, input_units, output):

lib/ramble/ramble/util/stats.py

@@ -92,6 +92,27 @@ def compute(self, values):
         return round(statistics.stdev(values), max_decimal_places(values))
 
 
+class StatsCoefficientOfVariation(StatsBase):
+    name = "cv"
+    min_count = 2
+
+    def compute(self, values):
+        mean = statistics.mean(values)
+        # Only guard against zero mean.
+        # While CV isn't particularly meaningful when negative values are present,
+        # calculate anyway and leave the interpretation to individual experiments.
+        if not mean:
+            return "NA"
+        return round(
+            statistics.stdev(values) / statistics.mean(values), max_decimal_places(values)
+        )
+
+    def get_unit(self, unit):
+        # `unit` unused
+        del unit
+        return ""
+
+
 class StatsCountValues(StatsBase):
     name = "n_successful_repeats"
 
@@ -109,5 +130,6 @@ def get_unit(self, unit):
     StatsMedian(),
     StatsVar(),
     StatsStdev(),
+    StatsCoefficientOfVariation(),
     StatsCountValues(),
 ]