[Numpy-discussion] Getting index of array after applying cond
Robert Kern
robert.kern@gmail....
Fri Apr 2 10:37:23 CDT 2010
On Fri, Apr 2, 2010 at 09:31, Shailendra <shailendra.vikas@gmail.com> wrote:
> Hi All,
> I have a following model problem. Let i have a array
>>>> x
> array([[1, 2, 3, 4, 5],
> [6, 7, 8, 7, 6],
> [1, 2, 3, 4, 5]])
>
> suppose i apply some cond on it.
>>>> cond= x>5
>>>> x[cond]
> array([6, 7, 8, 7, 6])
>
> Now, i want to argmax on this
>>>> max=argmax(x[cond])
>>>> max
> 2
>>>> x[cond][max]
> 8
> Now , I want to get the index of this element in x. How to acheive
> this. In real situation x will be huge.
In [1]: x = array([[1,2,3,4,5], [6,7,8,7,6], [1,2,3,4,5]])
In [2]: x
Out[2]:
array([[1, 2, 3, 4, 5],
[6, 7, 8, 7, 6],
[1, 2, 3, 4, 5]])
In [3]: cond = (x > 5)
In [4]: i, j = where(cond)
In [5]: i
Out[5]: array([1, 1, 1, 1, 1])
In [6]: j
Out[6]: array([0, 1, 2, 3, 4])
In [7]: argmax(x[cond])
Out[7]: 2
In [8]: i[2], j[2]
Out[8]: (1, 2)
In [9]: x[i[2], j[2]]
Out[9]: 8
--
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
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