X-Git-Url: https://wannabe.guru.org/gitweb/?a=blobdiff_plain;f=math_utils.py;h=156862a9c1b55eeec5515efef82f8f951d59b416;hb=89f305d67e913ea1512e2618a0375359ec925ada;hp=31610ba5fd2a0726b5b1f151dc87cc362b7389d4;hpb=14b42faebd598dc14cec6eaef77f06845e500b4b;p=python_utils.git

diff --git a/math_utils.py b/math_utils.py
index 31610ba..156862a 100644
--- a/math_utils.py
+++ b/math_utils.py
@@ -2,10 +2,13 @@
 
 """Mathematical helpers."""
 
+import collections
 import functools
 import math
 from heapq import heappop, heappush
-from typing import List, Optional
+from typing import Dict, List, Optional, Tuple
+
+import dict_utils
 
 
 class NumericPopulation(object):
@@ -25,7 +28,7 @@ class NumericPopulation(object):
     >>> pop.get_mean()
     5.2
     >>> round(pop.get_stdev(), 2)
-    6.99
+    1.75
     >>> pop.get_percentile(20)
     3
     >>> pop.get_percentile(60)
@@ -70,6 +73,14 @@ class NumericPopulation(object):
         count = len(self.lowers) + len(self.highers)
         return self.aggregate / count
 
+    def get_mode(self) -> Tuple[float, int]:
+        count: Dict[float, int] = collections.defaultdict(int)
+        for n in self.lowers:
+            count[-n] += 1
+        for n in self.highers:
+            count[n] += 1
+        return dict_utils.item_with_max_value(count)
+
     def get_stdev(self) -> float:
         """Returns the stdev so far in O(n) time."""
 
@@ -80,7 +91,8 @@ class NumericPopulation(object):
             variance += (n - mean) ** 2
         for n in self.highers:
             variance += (n - mean) ** 2
-        return math.sqrt(variance)
+        count = len(self.lowers) + len(self.highers) - 1
+        return math.sqrt(variance) / count
 
     def get_percentile(self, n: float) -> float:
         """Returns the number at approximately pn% (i.e. the nth percentile)