[Numpy-discussion] finding nonzero elements in list

Gökhan Sever gokhansever@gmail....
Mon Oct 12 09:39:59 CDT 2009


On Mon, Oct 12, 2009 at 9:18 AM, per freem <perfreem@gmail.com> wrote:

> hi all,
>
> i'm trying to find nonzero elements in an array, as follows:
>
> a = array([[1, 0],
>       [1, 1],
>       [1, 1],
>       [0, 1]])
>
> i want to find all elements that are [1,1]. i tried: nonzero(a ==
> [1,0]) but i cannot interpret the output. the output i get is:
> (array([0, 0, 1, 2]), array([0, 1, 0, 0]))
>
> i simply want to find the indices of the elements that equal [1,0].
> how can i do this? thanks.
>


You might simply apply a mask to your array satisfying the condition:

I[1]: a = array([[1, 0],
   ...:       [1, 1],
   ...:       [1, 1],
   ...:       [0, 1]])

I[2]: a == [1,0]
O[2]:
array([[ True,  True],
       [ True, False],
       [ True, False],
       [False, False]], dtype=bool)

I[3]: a[a==[1,0]]
O[3]: array([1, 0, 1, 1])


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-- 
Gökhan
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