[SciPy-user] "dynamic" indexing

Gerard Vermeulen gerard.vermeulen at grenoble.cnrs.fr
Thu Jun 10 02:48:58 CDT 2004


On Wed, 9 Jun 2004 15:27:32 -1000
"Addison, Jason" <JADDISON at SYSTEMS.TEXTRON.com> wrote:

> How can I take a slice from an array when I do not know before hand the 
> dimension of the source array? For example:
> 
> # slice is genereated dynamically, its length is not known before hand
> slice = [(2,4),(1,4),(0,15)]
> # then I'd like to somehow use slice to slice an array
> a[slice] -> a[2:4,1:4,0:15]
> 

Python-2.3 allows you to do

packer at zombie:~> python
Python 2.3+ (#1, Jan  7 2004, 09:17:35)
[GCC 3.3.1 (SuSE Linux)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> from scipy import *
>>> a = arange(35)
>>> a.shape = (7, 5)
>>> a
array([[ 0,  1,  2,  3,  4],
       [ 5,  6,  7,  8,  9],
       [10, 11, 12, 13, 14],
       [15, 16, 17, 18, 19],
       [20, 21, 22, 23, 24],
       [25, 26, 27, 28, 29],
       [30, 31, 32, 33, 34]])
>>> s0 = slice(0, 8, 2)
>>> s1 = slice(0, 6, 2)
>>> a[s0, s1]
array([[ 0,  2,  4],
       [10, 12, 14],
       [20, 22, 24],
       [30, 32, 34]])
>>>

See http://docs.python.org/whatsnew/section-slices.html

Gerard



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