X-Git-Url: https://wannabe.guru.org/gitweb/?a=blobdiff_plain;f=math_utils.py;h=f77e0a1f2514f5a0201c81f57e9740d36d2ede47;hb=d7d135be2f9dbb2d8398d7258f8bac24b4205a2b;hp=56fb7072366ab97621e032e9aed11d13d7740b5e;hpb=97fbe845e5dfdbda22521117c1783e1fd8515952;p=python_utils.git

diff --git a/math_utils.py b/math_utils.py
index 56fb707..f77e0a1 100644
--- a/math_utils.py
+++ b/math_utils.py
@@ -1,20 +1,42 @@
 #!/usr/bin/env python3
 
+"""Mathematical helpers."""
+
 import functools
 import math
+from heapq import heappop, heappush
 from typing import List
-from heapq import heappush, heappop
 
 
-class RunningMedian:
+class RunningMedian(object):
+    """A running median computer.
+
+    >>> median = RunningMedian()
+    >>> median.add_number(1)
+    >>> median.add_number(10)
+    >>> median.add_number(3)
+    >>> median.get_median()
+    3
+    >>> median.add_number(7)
+    >>> median.add_number(5)
+    >>> median.get_median()
+    5
+    >>> median.get_mean()
+    5.2
+    >>> round(median.get_stdev(), 2)
+    6.99
+    """
+
     def __init__(self):
         self.lowers, self.highers = [], []
+        self.aggregate = 0.0
 
-    def add_number(self, number):
+    def add_number(self, number: float):
         if not self.highers or number > self.highers[0]:
             heappush(self.highers, number)
         else:
             heappush(self.lowers, -number)  # for lowers we need a max heap
+        self.aggregate += number
         self.rebalance()
 
     def rebalance(self):
@@ -23,14 +45,28 @@ class RunningMedian:
         elif len(self.highers) - len(self.lowers) > 1:
             heappush(self.lowers, -heappop(self.highers))
 
-    def get_median(self):
+    def get_median(self) -> float:
         if len(self.lowers) == len(self.highers):
-            return (-self.lowers[0] + self.highers[0])/2
+            return (-self.lowers[0] + self.highers[0]) / 2
         elif len(self.lowers) > len(self.highers):
             return -self.lowers[0]
         else:
             return self.highers[0]
 
+    def get_mean(self) -> float:
+        count = len(self.lowers) + len(self.highers)
+        return self.aggregate / count
+
+    def get_stdev(self) -> float:
+        mean = self.get_mean()
+        variance = 0.0
+        for n in self.lowers:
+            n = -n
+            variance += (n - mean) ** 2
+        for n in self.highers:
+            variance += (n - mean) ** 2
+        return math.sqrt(variance)
+
 
 def gcd_floats(a: float, b: float) -> float:
     if a < b:
@@ -55,15 +91,69 @@ def gcd_float_sequence(lst: List[float]) -> float:
 
 
 def truncate_float(n: float, decimals: int = 2):
-    """Truncate a float to a particular number of decimals."""
-    assert decimals > 0 and decimals < 10
-    multiplier = 10 ** decimals
+    """
+    Truncate a float to a particular number of decimals.
+
+    >>> truncate_float(3.1415927, 3)
+    3.141
+
+    """
+    assert 0 < decimals < 10
+    multiplier = 10**decimals
     return int(n * multiplier) / multiplier
 
 
+def percentage_to_multiplier(percent: float) -> float:
+    """Given a percentage (e.g. 155%), return a factor needed to scale a
+    number by that percentage.
+
+    >>> percentage_to_multiplier(155)
+    2.55
+    >>> percentage_to_multiplier(45)
+    1.45
+    >>> percentage_to_multiplier(-25)
+    0.75
+
+    """
+    multiplier = percent / 100
+    multiplier += 1.0
+    return multiplier
+
+
+def multiplier_to_percent(multiplier: float) -> float:
+    """Convert a multiplicative factor into a percent change.
+
+    >>> multiplier_to_percent(0.75)
+    -25.0
+    >>> multiplier_to_percent(1.0)
+    0.0
+    >>> multiplier_to_percent(1.99)
+    99.0
+
+    """
+    percent = multiplier
+    if percent > 0.0:
+        percent -= 1.0
+    else:
+        percent = 1.0 - percent
+    percent *= 100.0
+    return percent
+
+
 @functools.lru_cache(maxsize=1024, typed=True)
 def is_prime(n: int) -> bool:
-    """Returns True if n is prime and False otherwise"""
+    """
+    Returns True if n is prime and False otherwise.  Obviously(?) very slow for
+    very large input numbers.
+
+    >>> is_prime(13)
+    True
+    >>> is_prime(22)
+    False
+    >>> is_prime(51602981)
+    True
+
+    """
     if not isinstance(n, int):
         raise TypeError("argument passed to is_prime is not of 'int' type")
 
@@ -75,12 +165,18 @@ def is_prime(n: int) -> bool:
 
     # This is checked so that we can skip middle five numbers in below
     # loop
-    if (n % 2 == 0 or n % 3 == 0):
+    if n % 2 == 0 or n % 3 == 0:
         return False
 
     i = 5
     while i * i <= n:
-        if (n % i == 0 or n % (i + 2) == 0):
+        if n % i == 0 or n % (i + 2) == 0:
             return False
         i = i + 6
     return True
+
+
+if __name__ == '__main__':
+    import doctest
+
+    doctest.testmod()