you are right Eric, In [405]: b[...,-4:] Out[405]: array([[ 6, 7, 8, 9], [16, 17, 18, 19]]) cheers, Chao 2011/10/18 Chao YUE <chaoyuejoy@gmail.com>

Thanks Jean I just want the last several numbers by indexing from the end.

In [400]: b=np.arange(20).reshape(2,10)

In [401]: b Out[401]: array([[ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9], [10, 11, 12, 13, 14, 15, 16, 17, 18, 19]])

I want something like b[...,...(index from the end by using negative number)] to get: array([[ 6, 7, 8, 9], [16, 17, 18, 19]])

but it's strange that if you use b[...,-1], you get: In [402]: b[...,-1] Out[402]: array([ 9, 19])

if use b[...,-4:-1], you get: Out[403]: array([[ 6, 7, 8], [16, 17, 18]])

but you cannot use b[...,-4:-1] to get array([[ 6, 7, 8, 9], [16, 17, 18, 19]]) because In [403]: b[...,-4:-1] Out[403]: array([[ 6, 7, 8], [16, 17, 18]])

I don't know I am more clear this time....

Chao

2011/10/18 Jean-Luc Menut <jeanluc.menut@free.fr>

...

how can I pick up something like:

...

array([[1, 2, 3, 4], [6, 7, 8, 9]])

I'm not sure to understand, should not a[:,1:] be sufficient ? Did I miss something in your message ?

--

*********************************************************************************** Chao YUE Laboratoire des Sciences du Climat et de l'Environnement (LSCE-IPSL) UMR 1572 CEA-CNRS-UVSQ Batiment 712 - Pe 119 91191 GIF Sur YVETTE Cedex Tel: (33) 01 69 08 29 02; Fax:01.69.08.77.16

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-- *********************************************************************************** Chao YUE Laboratoire des Sciences du Climat et de l'Environnement (LSCE-IPSL) UMR 1572 CEA-CNRS-UVSQ Batiment 712 - Pe 119 91191 GIF Sur YVETTE Cedex Tel: (33) 01 69 08 29 02; Fax:01.69.08.77.16 ************************************************************************************

thanks Scott. very good explanation. cheers, Chao 2011/10/18 Scott Sinclair <scott.sinclair.za@gmail.com>

On 18 October 2011 13:56, Chao YUE <chaoyuejoy@gmail.com> wrote:

...

but it's strange that if you use b[...,-1], you get: In [402]: b[...,-1] Out[402]: array([ 9, 19])

if use b[...,-4:-1], you get: Out[403]: array([[ 6, 7, 8], [16, 17, 18]])

That's because you're mixing two different indexing constructs. In the first case, you're using direct indexing, so you get the values in b at the index you specify.

In the second example you're using slicing syntax, where you get the values in b at the range of indices starting with -4 and ending *one before* -1 i.e. the values at b[..., -2].

Here's a simpler example:

In [1]: a = range(5)

In [2]: a Out[2]: [0, 1, 2, 3, 4]

In [3]: a[0] Out[3]: 0

In [4]: a[2] Out[4]: 2

In [5]: a[0:2] Out[5]: [0, 1]

In [6]: a[-3] Out[6]: 2

In [7]: a[-1] Out[7]: 4

In [8]: a[-3:-1] Out[8]: [2, 3]

Cheers, Scott _______________________________________________ NumPy-Discussion mailing list NumPy-Discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion

-- *********************************************************************************** Chao YUE Laboratoire des Sciences du Climat et de l'Environnement (LSCE-IPSL) UMR 1572 CEA-CNRS-UVSQ Batiment 712 - Pe 119 91191 GIF Sur YVETTE Cedex Tel: (33) 01 69 08 29 02; Fax:01.69.08.77.16 ************************************************************************************