# [Numpy-discussion] index of a value in an array

Jonathan Rocher jrocher@enthought....
Wed Oct 6 09:48:32 CDT 2010

```Chris,

Note that
>>> where(condition)
actually returns a tuple (one item for each dimension of a) and each element
is an array with the index of when your condition occurs.
Therefore if you want to extract the index itself, you need to write
idx = where(a==1)[0][0] for the first element, and where(a==1)[0] for the
array of all indices.

Best,
Jonathan

On Wed, Oct 6, 2010 at 8:53 AM, Thomas, Brian (GE Energy) <
brian1.thomas@ge.com> wrote:

> Chris,
>
> You can use where() command to find index of a particular number in the
> array.
>
> For e.g. to find index of number 1 in array a, you can say
> idx = where(a==1)
>
> Regards,
> Brian
>
> -----Original Message-----
> From: numpy-discussion-bounces@scipy.org
> [mailto:numpy-discussion-bounces@scipy.org] On Behalf Of Chris Withers
> Sent: Wednesday, October 06, 2010 5:27 AM
> To: numpy-discussion@scipy.org
> Cc: snezana.pejic@glcuk.com
> Subject: [Numpy-discussion] index of a value in an array
>
> Hi All,
>
> Given an array such as:
>
> array([0, 1, 2, 3, 4, 5, 6, 7, 8, 9])
>
> How can I find the index of a particular number in the array?
>
> (ie: if it was a list, I'd do [1,2,3,4].index(3))
>
> cheers,
>
> Chris
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--
Jonathan Rocher,
Enthought, Inc.
jrocher@enthought.com
1-512-536-1057
http://www.enthought.com
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