[Numpy-discussion] fancy indexing/broadcasting question

Mark.Miller mpmusu@cc.usu....
Sat Jul 7 13:41:22 CDT 2007


Sorry...here's a minor correction to the code.

#1st part
import numpy
normal=numpy.random.normal

RNDarray = normal(25,15,(50,50))
tmp1 = (RNDarray < 0) | (RNDarray > 25)
while tmp1.any():
     print tmp1.size, tmp1.shape, tmp1[tmp1].size
     RNDarray[tmp1] = normal(25,15, size = RNDarray[tmp1].size)
     tmp1 = (RNDarray < 0) | (RNDarray > 25)

#2nd part
import numpy
normal=numpy.random.normal

RNDarray = normal(25,15,(50,50))
tmp1 = (RNDarray < 0) | (RNDarray > 25)
while tmp1.any():
     print tmp1.size, tmp1.shape, tmp1[tmp1].size
     RNDarray[tmp1] = normal(25,15, size = RNDarray[tmp1].size)
*   tmp1 = (RNDarray[tmp1] < 0) | (RNDarray[tmp1] > 25)

Mark.Miller wrote:
> A quick question for the group.  I'm working with some code to generate 
> some arrays of random numbers.  The random numbers, however, need to 
> meet certain criteria.  So for the moment, I have things that look like 
> this (code is just an abstraction):
> 
> import numpy
> normal=numpy.random.normal
> 
> RNDarray = normal(25,15,(50,50))
> tmp1 = (RNDarray < 0) | (RNDarray > 25)
> while tmp1.any():
>      print tmp1.size, tmp1.shape, tmp1[tmp1].size
>      RNDarray[tmp1] = normal(5,3, size = RNDarray[tmp1].size)
>      tmp1 = (RNDarray < 0) | (RNDarray > 25)
> 
> This code works well.  However, it might be considered inefficient 
> because, for each iteration of the while loop, all values get 
> reevaluated even if they have previously met the criteria encapsulated 
> in tmp1.  It would be better if, for each cycle of the while loop, only 
> those elements that have previously not met criteria get reevaluated.
> 
> I tried a few things that haven't worked.  An example is provided below 
> (changed code marked with *):
> 
> RNDarray = normal(25,15,(50,50))
> tmp1 = (RNDarray < 0) | (RNDarray > 25)
> while tmp1.any():
>      print tmp1.size, tmp1.shape, tmp1[tmp1].size
>      RNDarray[tmp1] = normal(5,3, size = RNDarray[tmp1].size)
> *   tmp1 = (RNDarray[tmp1] < 0) | (RNDarray[tmp1] > 25)
> 
> I see why this doesn't work properly.  When tmp1 is reevaluated in the 
> while loop, it returns an array with a different shape.
> 
> Does anyone have any suggestions for improvement here?  Please let me 
> know if any of this requires clarification.
> 
> Thanks,
> 
> -Mark
> _______________________________________________
> Numpy-discussion mailing list
> Numpy-discussion@scipy.org
> http://projects.scipy.org/mailman/listinfo/numpy-discussion

-- 
Dr. Mark P. Miller
Department of Biology
5305 Old Main Hill
Utah State University
Logan, UT 84322-5305 USA
 ><><><><><><><><><><><><><><><><
http://www.biology.usu.edu/people/facultyinfo.asp?username=mpmbio
http://www.marksgeneticsoftware.net


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