Dear all, I am new to the Numpy-discussion list. I would like to follow up some possibly useful information about calculating median. The message below was posted today on the AstroPy mailing list. Kind regards Jerome Caron
#---------------------------------------- I think the calculation of median values in Numpy is not optimal. I don't know if there are other libraries that do better? On my machine I get these results: >>> data = numpy.random.rand(5000,5000) >>> t0=time.time();print numpy.ma.median(data);print time.time()-t0 0.499845739822 15.1949999332 >>> t0=time.time();print numpy.median(data);print time.time()-t0 0.499845739822 4.32100009918 >>> t0=time.time();print aspylib.astro.get_median(data);print time.time()-t0 [ 0.49984574] 0.90499997139 >>> The median calculation in Aspylib is using C code from Nicolas Devillard (can be found here: http://ndevilla.free.fr/median/index.html) interfaced with ctypes. It could be easily re-used for other, more official packages. I think the code also finds quantiles efficiently. See: http://www.aspylib.com/
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