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amix/sorts.py

Created March 19, 2016 11:10
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The confidence sort in pure Python (from Reddit's codebase)
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sorts.py
# Rewritten code from /r2/r2/lib/db/_sorts.pyx
from math import sqrt
def _confidence(ups, downs):
n = ups + downs
if n == 0:
return 0
z = 1.281551565545
p = float(ups) / n
left = p + 1/(2*n)*z*z
right = z*sqrt(p*(1-p)/n + z*z/(4*n*n))
under = 1+1/n*z*z
return (left - right) / under
def confidence(ups, downs):
if ups + downs == 0:
return 0
else:
return _confidence(ups, downs)
@peanutbother
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peanutbother commented May 30, 2016 •
edited
Loading 

def confidence(ups, downs):
    if ups + downs == 0:
        return 0

this is double work; because

def _confidence(ups, downs):
    n = ups + downs
    if n == 0:
        return 0

already does that.

you should remove confidence and rename _confidence to confidence
see my fork for a better understanding: https://gist.github.com/jay-bricksoft/fdd3797b1443153389d34a4b5280ac54
cheers

@phoglenix
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In python2 x/y is integer division, so line #13 and #15 will be incorrect.
Easily fixed by moving the z*z to the left of the division.

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