[Numpy-discussion] Set values of a matrix within a specified range to zero

Ryan May rmay31@gmail....
Tue Mar 30 16:35:16 CDT 2010

On Tue, Mar 30, 2010 at 3:16 PM, Friedrich Romstedt
<friedrichromstedt@gmail.com> wrote:
> 2010/3/30 Ryan May <rmay31@gmail.com>:
>> On Tue, Mar 30, 2010 at 11:12 AM, Alan G Isaac <aisaac@american.edu> wrote:
>>> On 3/30/2010 12:56 PM, Sean Mulcahy wrote:
>>>> 512x512 arrays.  I would like to set elements of the array whose value fall within a specified range to zero (eg 23<  x<  45).
>>> x[(23<x)*(x<45)]=0
>> Or a version that seems a bit more obvious (doing a multiply between
>> boolean arrays to get an AND operator seems a tad odd):
>> x[(23<x) & (x<45)] = 0
> We recently found out that it executes faster using:
> x *= ((x <= 23) | (x >= 45))  .

Interesting. In an ideal world, I'd love to see why exactly that is,
because I don't think multiplication should be faster than a boolean
op.  If you need speed, then by all means go for it.  But if you don't
need speed I'd use the & since that will be more obvious to the person
who ends up reading your code later and has to spend time decoding
what that line does.


Ryan May
Graduate Research Assistant
School of Meteorology
University of Oklahoma

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