[Numpy-discussion] Putmask/take ?
Robert Kern
robert.kern at gmail.com
Fri Sep 22 02:17:57 CDT 2006
Stefan van der Walt wrote:
> Hi P.,
>
> On Thu, Sep 21, 2006 at 07:40:39PM -0400, PGM wrote:
>
>> I'm running into the following problem with putmask on take.
>>
>>>>> import numpy
>>>>> x = N.arange(12.)
>>>>> m = [1, 0, 0, 0, 0, 0, 1, 0, 0, 1, 0, 1]
>>>>> i = N.nonzero(m)[0]
>>>>> w = N.array([-1, -2, -3, -4.])
>>>>> x.putmask(w,m)
>>>>> x.take(i)
>>>>> N.allclose(x.take(i),w)
>
> According to the putmask docstring:
>
> a.putmask(values, mask) sets a.flat[n] = v[n] for each n where
> mask.flat[n] is true. v can be scalar.
>
> This would mean that 'w' is not of the right length.
There are 4 true values in m and 4 values in w. What's the wrong length?
For the sake of clarity:
In [1]: from numpy import *
In [3]: m = [1, 0, 0, 0, 0, 0, 1, 0, 0, 1, 0, 1]
In [4]: i = nonzero(m)[0]
In [5]: i
Out[5]: array([ 0, 6, 9, 11])
In [6]: w = array([-1, -2, -3, -4.])
In [7]: x = arange(12.)
In [8]: x.putmask(w, m)
In [9]: x
Out[9]:
array([ -1., 1., 2., 3., 4., 5., -3., 7., 8., -2., 10.,
-4.])
In [17]: x[array(m, dtype=bool)] = w
In [18]: x
Out[18]:
array([ -1., 1., 2., 3., 4., 5., -2., 7., 8., -3., 10.,
-4.])
Out[9] and Out[18] should have been the same, but elements 6 and 9 are flipped.
It's pretty clear that this is a bug in .putmask().
--
Robert Kern
"I have come to believe that the whole world is an enigma, a harmless enigma
that is made terrible by our own mad attempt to interpret it as though it had
an underlying truth."
-- Umberto Eco
More information about the Numpy-discussion
mailing list