[Numpy-discussion] fancy indexing/broadcasting question
Anne Archibald
peridot.faceted@gmail....
Sat Jul 7 14:13:59 CDT 2007
On 07/07/07, Mark.Miller <mpmusu@cc.usu.edu> 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.
You can write a quick recursive function to do it:
In [33]: def gen_condition(n):
....: A = normal(size=n)
....: c = abs(A)>1
....: subn = sum(c)
....: if subn>0:
....: A[c] = gen_condition(subn)
....: return A
....:
Probably not ideal if it's going to take many tries, but it's pretty clear.
Anne
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