[Numpy-discussion] Comparison of arrays
Brent Pedersen
bpederse@gmail....
Mon Feb 9 10:22:35 CST 2009
On Mon, Feb 9, 2009 at 6:02 AM, Neil <neilcrighton@gmail.com> wrote:
>
>> > I have two integer arrays of different shape, e.g.
>> >
>> > >>> a
>> >
>> > array([ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10])
>> >
>> > >>> b
>> >
>> > array([ 3, 4, 5, 6, 7, 8, 9, 10])
>> >
>> > How can I extract the values that belong to the array a
>> > exclusively i.e. array([1,2]) ?
>>
>
> You could also use numpy.setmember1d to get a boolean mask that selects
> the values:
>
> In [21]: a = np.array([ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10])
> In [22]: b = np.array([ 3, 4, 5, 6, 7, 8, 9, 10])
> In [23]: ismember = np.setmember1d(a,b)
> In [24]: a[~ismember]
> Out[24]: array([1, 2])
>
>
> Neil
>
>
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>
there's also np.setdiff1d() which does the above in a single line.
-brent
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