[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
More information about the Numpy-discussion
mailing list