Nadav Horesh wrote: > I think you need to use masked arrays. > > Nadav > > > -----הודעה מקורית----- > מאת: [EMAIL PROTECTED] בשם Peter Saffrey > נשלח: ה 18-ספטמבר-08 14:27 > אל: numpy-discussion@scipy.org > נושא: [Numpy-discussion] Medians that ignore values > > I have data from biological experiments that is represented as a list of > about 5000 triples. I would like to convert this to a list of the median > of each triple. I did some profiling and found that numpy was much about > 12 times faster for this application than using regular Python lists and > a list median implementation. I'll be performing quite a few > mathematical operations on these values, so using numpy arrays seems > sensible. > > The only problem is that my data has gaps in it - where an experiment > failed, a "triple" will not have three values. Some will have 2, 1 or > even no values. To keep the arrays regular so that they can be used by > numpy, is there some dummy value I can use to fill these gaps that will > be ignored by the median routine? > > I tried NaN for this, but as far as median is concerned, it counts as > infinity: > > >>> from numpy import * > >>> median(array([1,3,nan])) > 3.0 > >>> median(array([1,nan,nan])) > nan > > Is this the correct behavior for median with nan? Is there a fix for > this or am I going to have to settle with using lists? > > Thanks, > > Peter > _______________________________________________ > Numpy-discussion mailing list > Numpy-discussion@scipy.org > http://projects.scipy.org/mailman/listinfo/numpy-discussion > > > ------------------------------------------------------------------------ > > _______________________________________________ > Numpy-discussion mailing list > Numpy-discussion@scipy.org > http://projects.scipy.org/mailman/listinfo/numpy-discussion > Hi, The counting of infinity is correct due to the implementation of IEEE Standard for Binary Floating-Point for Arithmetic (IEEE 754).
You might want to try isfinite() to first remove nan, +/- infinity before doing that. numpy.median(a[numpy.isfinite(a)]) Bruce _______________________________________________ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
