Created
March 19, 2016 11:10
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The confidence sort in pure Python (from Reddit's codebase)
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| # 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) |
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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.