Add median adjustment for even length arrays (#2132)

Add median adjustment for even length arrays
graphite-project · Nov 28, 2017 · 61ac7f2 · 61ac7f2
1 parent d4eb9cc
commit 61ac7f2
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Showing 2 changed files with 12 additions and 4 deletions.
diff --git a/webapp/graphite/render/functions.py b/webapp/graphite/render/functions.py
@@ -97,7 +97,12 @@ def safeAvg(values):
 def safeMedian(values):
   safeValues = [v for v in values if v is not None]
   if safeValues:
-    return sorted(safeValues)[len(safeValues) // 2]
+    sortedVals = sorted(safeValues)
+    mid = len(sortedVals) // 2
+    if len(sortedVals) % 2 == 0:
+      return float(sortedVals[mid-1] + sortedVals[mid]) / 2
+    else:
+      return sortedVals[mid]
 
 def safeStdDev(a):
   sm = safeSum(a)

diff --git a/webapp/tests/test_functions.py b/webapp/tests/test_functions.py
@@ -193,14 +193,17 @@ def test_safeMedian_None(self):
     def test_safeMedian_empty_list(self):
         self.assertEqual(functions.safeMedian([]), None)
 
-    def test_safeMedian_all_numbers(self):
-        self.assertEqual(functions.safeMedian([1,2,3,4]), 3)
+    def test_safeMedian_all_numbers_odd_len(self):
+        self.assertEqual(functions.safeMedian([1,2,3,4,5]), 3)
+
+    def test_safeMedian_all_numbers_even_len(self):
+        self.assertAlmostEqual(functions.safeMedian([1,2,3,4]), 2.5)
 
     def test_safeMedian_all_None(self):
         self.assertEqual(functions.safeMedian([None,None,None,None]), None)
 
     def test_safeMedian_mixed(self):
-        self.assertEqual(functions.safeMedian([10,None,5,None]), 10)
+        self.assertAlmostEqual(functions.safeMedian([10,None,5,None]), 7.5)
 
     #
     # Test safeStdDev()