[Numpy-discussion] Generalize hstack/vstack --> stack; Block matrices like in matlab

Eelco Hoogendoorn hoogendoorn.eelco at gmail.com
Mon Sep 8 12:41:58 EDT 2014


Sturla: im not sure if the intention is always unambiguous, for such more
flexible arrangements.

Also, I doubt such situations arise often in practice; if the arrays arnt a
grid, they are probably a nested grid, and the code would most naturally
concatenate them with nested calls to a stacking function.

However, some form of nd-stack function would be neat in my opinion.

On Mon, Sep 8, 2014 at 6:10 PM, Jaime Fernández del Río <
jaime.frio at gmail.com> wrote:

> On Mon, Sep 8, 2014 at 7:41 AM, Sturla Molden <sturla.molden at gmail.com>
> wrote:
>
>> Stefan Otte <stefan.otte at gmail.com> wrote:
>>
>> >     stack([[a, b], [c, d]])
>> >
>> > In my case `stack` replaced `hstack` and `vstack` almost completely.
>> >
>> > If you're interested in including it in numpy I created a pull request
>> > [1]. I'm looking forward to getting some feedback!
>>
>> As far as I can see, it uses hstack and vstack. But that means a and b
>> have
>> to have the same number of rows, c and d must have the same rumber of
>> rows,
>> and hstack((a,b)) and hstack((c,d)) must have the same number of columns.
>>
>> Thus it requires a regularity like this:
>>
>> AAAABB
>> AAAABB
>> CCCDDD
>> CCCDDD
>> CCCDDD
>> CCCDDD
>>
>> What if we just ignore this constraint, and only require the output to be
>> rectangular? Now we have a 'tetris game':
>>
>> AAAABB
>> AAAABB
>> CCCCBB
>> CCCCBB
>> CCCCDD
>> CCCCDD
>>
>> or
>>
>> AAAABB
>> AAAABB
>> CCCCBB
>> CCCCBB
>> CCCCBB
>> CCCCBB
>>
>> This should be 'stackable', yes? Or perhaps we need another stacking
>> function for this, say numpy.tetris?
>>
>> And while we're at it, what about higher dimensions? should there be an
>> ndstack function too?
>>
>
> This is starting to look like the second time in a row Stefan tries to
> extend numpy with a simple convenience function, and he gets tricked into
> implementing some sophisticated algorithm...
>
> For his next PR I expect nothing less than an NP-complete problem. ;-)
>
>
>> Jaime
>
> --
> (\__/)
> ( O.o)
> ( > <) Este es Conejo. Copia a Conejo en tu firma y ayúdale en sus planes
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