[Numpy-discussion] Slicing with index lists
Robert Kern
robert.kern@gmail....
Thu Apr 12 03:43:19 CDT 2007
Bernhard Voigt wrote:
> Dear all!
>
> in a 2-dim array I would like to select rows specified by a list of
> indexes and from these rows I'd like to select columns specified by
> another list of indexes. That's what I found as a solution:
>
> In [90]: a = arange(15).reshape(5,3)
> In [91]: a
> Out[91]:
> array([[ 0, 1, 2],
> [ 3, 4, 5],
> [ 6, 7, 8],
> [ 9, 10, 11],
> [12, 13, 14]])
>
> # select rows 1,3,4 and columns 0,2
>
> In[92]: a[[1,3,4],:][:,[0,2]]
> Out[92]:
> array([[ 3, 5],
> [ 9, 11],
> [12, 14]])
>
> Is there a better way to express this selection? I thought there might
> be single slicing expression for this, but I couldn't figure it out :-(
In [3]: from numpy import *
In [4]: a = arange(15).reshape(5,3)
In [5]: a[ix_([1,3,4], [0,2])]
Out[5]:
array([[ 3, 5],
[ 9, 11],
[12, 14]])
--
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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