[Numpy-discussion] How do I do this?

Keith Goodman kwgoodman@gmail....
Fri Aug 29 16:52:47 CDT 2008


On Fri, Aug 29, 2008 at 2:49 PM, Keith Goodman <kwgoodman@gmail.com> wrote:
> On Fri, Aug 29, 2008 at 2:35 PM, Christopher Barker
> <Chris.Barker@noaa.gov> wrote:
>> HI all,
>>
>> I need to do something I thought would be simple -- set all the values
>> of an array to some minimum. so I did this:
>>
>>  >>> min_value = 2
>>  >>> a = np.array((1, 2, 3, 4, 5,))
>>  >>> np.maximum(a, min_value)
>> array([2, 2, 3, 4, 5])
>>
>> all was well... then I realized that a could have negative numbers in
>> in, and I really wanted the absolute value to be greater than than minimum:
>>
>>  >>> a = np.array((1, 2, 3, 4, -5,))
>>  >>> np.maximum(a, min_value)
>> array([2, 2, 3, 4, 2])
>>
>> oops!
>>
>> so I added a sign() and abs():
>>
>>  >>> np.sign(a) * np.maximum(np.abs(a), min_value)
>> array([ 2,  2,  3,  4, -5])
>>
>> all was well. However it turns out a could contain a zero:
>>
>>  >>> a = np.array((0, 1, 2, 3, 4, -5,))
>>  >>> np.sign(a) * np.maximum(np.abs(a), min_value)
>> array([ 0,  2,  2,  3,  4, -5])
>>
>> Darn! I want that zero to become a 2, but sign(0)  = 0, so that doesn't
>> work.
>>
>> How can I do this without another line of code special casing the 0,
>> which isn't that big I deal, but it seems kind of ugly...
>>
>>  >>> a[a==0] = min_value
>>  >>> np.sign(a) * np.maximum(np.abs(a), min_value)
>> array([ 2,  2,  2,  3,  4, -5])
>
> Does this work?
>
>>> x
>   array([ 1.,  2., -5., -1.,  0.])
>>> np.sign(x) * np.clip(np.absolute(x), 2, np.inf)
>   array([ 2.,  2., -5., -2.,  0.])

Oh, I guess 0 is less than 2.


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