[Numpy-discussion] Strange behavior with boolean slices...

[Eric Firing]

On 2013/08/25 2:30 PM, Cera, Tim wrote:
> I have done this before, but am now really confused.
>
> Created an array 'day' specifying the 'f' type
>
> In [29]: day
> Out[29]: array([ 5.,  5.], dtype=float32)
>
> # Have a mask...
> In [30]: mask
> Out[30]: array([ True, False], dtype=bool)
>
> # So far, so good...
> In [31]: day[mask]
> Out[31]: array([ 5.], dtype=float32)
>
> In [32]: day[mask] = 10
>
> # What?
> In [33]: day
> Out[33]: array([ 10.,  10.], dtype=float32)
>

I don't get it with 1.7.1, either:

In [2]: np.__version__
Out[2]: '1.7.1'

In [3]: %paste
mask = np.array([True, False], dtype=bool)
day = np.array([5, 5], dtype=np.float32)
day
mask
day[mask]
day[mask] = 10
day
## -- End pasted text --
Out[3]: array([ 10.,   5.], dtype=float32)

My 1.7.0 example is on a Mac, the 1.7.1 is on a Linux virtual machine, 
both 64-bit.

Eric

>
> So I created an integer array 'a'
>
> In [38]: a
> Out[38]: array([11,  1])
>
> In [39]: a[mask]
> Out[39]: array([11])
>
> In [40]: a[mask] = 12
>
> # This is what I expect.
> In [41]: a
> Out[41]: array([12,  1])
>
> Am I missing something?  Is this supposed to happen?
>
> Version 1.7.1.
>
> Kindest regards,
> Tim
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