[Numpy-discussion] Slicing/selection in multiple dimensions simultaneously

Robert Kern robert.kern@gmail....
Mon Mar 2 11:25:24 CST 2009


On Mon, Mar 2, 2009 at 04:19, David Warde-Farley <dwf@cs.toronto.edu> wrote:
> On 28-Feb-09, at 12:27 PM, Jonathan Taylor wrote:
>
>> This does seem like the only way to write this nicely.  Unfortunately,
>> I think this may be wasteful memory wise (in contrast to what the
>> obvious matlab code would do) as it constructs an array with the whole
>> first index intact at first.
>
> True enough, though if I understand correctly, this is only a _view_
> onto the original array, and nothing is immediately copied. So it does
> waste memory creating a view and then a view on the view, but I don't
> think it's proportional to the size of the returned array.

a[[2,3,6], ...][..., [3,2]]

You're doing fancy indexing, so there are copies both times.

-- 
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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