[issue21592] Make statistics.median run in linear time
Dong-hee Na
report at bugs.python.org
Mon May 7 09:25:03 EDT 2018
Dong-hee Na <donghee.na92 at gmail.com> added the comment:
For CPython, I agree with the opinion that finding a median value with Tim sort(C version) is faster than quickselect algorithm with pure python.
Or we need to implement quickselect by C API.
The advantage of implementing this method by quickselect with pure python will be for pypy or any other python compatible compiler.
Considering the role that CPython provides for the standard library to other compatible compilers, it is worth considering from a performance point of view with a compatible compiler. However, for CPython, we have to take a performance hit.
Here is the benchmark result with pypy3 on MacOS
N sort select7 select23 select47 select97 select select2 PR6715
-------- -------- -------- -------- -------- -------- -------- ------- -------
5000 0.000 0.003 0.000 0.000 0.000 0.001 0.001 0.001
10000 0.000 0.001 0.001 0.001 0.001 0.000 0.000 0.001
50000 0.002 0.005 0.004 0.002 0.002 0.000 0.000 0.000
100000 0.005 0.008 0.004 0.004 0.005 0.001 0.001 0.001
500000 0.027 0.021 0.016 0.019 0.021 0.004 0.003 0.003
1000000 0.054 0.035 0.030 0.037 0.041 0.006 0.007 0.008
2000000 0.104 0.069 0.063 0.074 0.084 0.013 0.013 0.015
3000000 0.162 0.105 0.091 0.109 0.122 0.017 0.018 0.017
4000000 0.219 0.137 0.122 0.148 0.167 0.024 0.016 0.024
5000000 0.275 0.170 0.156 0.182 0.204 0.030 0.028 0.017
6000000 0.336 0.210 0.181 0.220 0.247 0.030 0.039 0.040
7000000 0.447 0.283 0.242 0.292 0.329 0.056 0.055 0.043
8000000 0.503 0.309 0.248 0.313 0.338 0.051 0.049 0.052
9000000 0.592 0.359 0.323 0.353 0.421 0.065 0.047 0.082
10000000 0.643 0.398 0.357 0.412 0.433 0.061 0.070 0.047
11000000 0.700 0.387 0.365 0.454 0.459 0.087 0.075 0.077
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nosy: +corona10
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<https://bugs.python.org/issue21592>
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