Slicing matrix

[Robert Kern]

Anthony Liu wrote:
> I am using numarray.

I will be using numpy for this post, and if you are new to numarray, then you
should probably skip it and use numpy instead. All new development is going
towards numpy.

  http://numeric.scipy.org/

> Suppose I have
> 
>>>>p = array(range(25), shape=(5,5))
>>>>p
> 
> 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]])

In [4]: from numpy import *

In [5]: p = arange(25).reshape((5,5))

In [6]: p
Out[6]:
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]])

> How do I easily slice out [0,1,2]

In [7]: p[0, :3]
Out[7]: array([0, 1, 2])

> or [1,2,3]

In [9]: p[0, 1:4]
Out[9]: array([1, 2, 3])

> or [2,7,12]

In [10]: p[:3, 2]
Out[10]: array([ 2,  7, 12])

> or [7,12,17] and put it in a list?

In [11]: p[1:4, 2]
Out[11]: array([ 7, 12, 17])

-- 
Robert Kern
robert.kern at gmail.com

"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