[Numpy-discussion] Re: [SciPy-dev] unique hanging?

Jonathan Taylor jonathan.taylor at stanford.edu
Tue Mar 14 20:32:01 CST 2006


thanks for the reply.

i could be wrong, but this problem seemed to appear only when i updated 
svn -- i had a very similar
example before with N.nan that seemed fine....

-- jonathan

Sasha wrote:

>This really belongs to numpy-discussion.
>
>What you observe is probably the consequence of nan not being equal to itself:
>
>  
>
>>>>N.equal(N.nan,N.nan)
>>>>        
>>>>
>False
>
>Many algorithms would fail to terminate or produce wrong results when
>they encounter such an anomaly.
>
>For example:
>
>  
>
>>>>N.sort([N.nan,5, N.nan, 3])
>>>>        
>>>>
>array([        nan,  5.        ,         nan,  3.        ])
>
>This is unfortunate, but not really a bug.  I would suggest that we
>document which numpy functions are nan safe and which are not.
>
>
>
>On 3/14/06, Jonathan Taylor <jonathan.taylor at stanford.edu> wrote:
>  
>
>>hi all,
>>
>>apologize if this is not the right list -- in the latest svn of numpy
>>unique seems to be taking a long time with "nan"
>>
>>reproducible error:
>>
>>-------------------------------------------------------------------------------------------
>>import numpy as N
>>import numpy.random as R
>>
>>x = R.standard_normal((100000,))
>>x = N.around(x * 100.) / 100.
>>
>>print len(N.unique(x))
>>
>>x[0] = N.nan
>>print len(N.unique(x))
>>
>>
>>x[0:50000] = N.nan
>>print 'OK'
>>
>>print len(N.unique(x))
>>
>>
>>--
>>------------------------------------------------------------------------
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>>------------------------------------------------------------------------
>>Jonathan Taylor                           Tel:   650.723.9230
>>Dept. of Statistics                       Fax:   650.725.8977
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>>
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>>
>>
>>
>>    
>>

-- 
------------------------------------------------------------------------
I'm part of the Team in Training: please support our efforts for the
Leukemia and Lymphoma Society!

http://www.active.com/donate/tntsvmb/tntsvmbJTaylor

GO TEAM !!!

------------------------------------------------------------------------
Jonathan Taylor                           Tel:   650.723.9230
Dept. of Statistics                       Fax:   650.725.8977
Sequoia Hall, 137                         www-stat.stanford.edu/~jtaylo
390 Serra Mall
Stanford, CA 94305





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