numpy-discussion

[Numpy-discussion] Helper function to "unroll" a array

[Gael V. <gae...@no...>]

Hi,

There is an operation I do a lot, I would call it "unrolling" a array.
The best way to describe it is probably to give the code:

def unroll(M):
    """ Flattens the array M and returns a 2D array with the first column=
s=20
	being the indices of M, and the last column the flatten M.
    """
    return hstack((indices(M.shape).reshape(-1,M.ndim),M.reshape(-1,1)))

Example:

>>> M
array([[ 0.73530097,  0.3553424 ,  0.3719772 ],
       [ 0.83353373,  0.74622133,  0.14748905],
       [ 0.72023762,  0.32306969,  0.19142366]])

>>> unroll(M)
array([[ 0.        ,  0.        ,  0.73530097],
       [ 0.        ,  1.        ,  0.3553424 ],
       [ 1.        ,  1.        ,  0.3719772 ],
       [ 2.        ,  2.        ,  0.83353373],
       [ 2.        ,  0.        ,  0.74622133],
       [ 1.        ,  2.        ,  0.14748905],
       [ 0.        ,  1.        ,  0.72023762],
       [ 2.        ,  0.        ,  0.32306969],
       [ 1.        ,  2.        ,  0.19142366]])


The docstring sucks. The function is trivial (when you know numpy a bit).
Maybe this function already exists in numpy, if so I couldn't find it.
Elsewhere I propose it for inclusion.

Cheers,

Ga=EBl

Re: [Numpy-discussion] Helper function to "unroll" a array

[Gael V. <gae...@no...>]

    Hi all,

I didn't get any answers to this email. Is it because the proposed
addition to numpy is not of any interest to anybody apart from me ?
Maybe the way I introduced this is wrong. Please tell me what is wrong
with this proposition.

Regards,

Ga=EBl

On Fri, Oct 20, 2006 at 01:28:52PM +0200, Gael Varoquaux wrote:
> Hi,

> There is an operation I do a lot, I would call it "unrolling" a array.
> The best way to describe it is probably to give the code:

> def unroll(M):
>     """ Flattens the array M and returns a 2D array with the first colu=
mns=20
> 	being the indices of M, and the last column the flatten M.
>     """
>     return hstack((indices(M.shape).reshape(-1,M.ndim),M.reshape(-1,1))=
)

> Example:

> >>> M
> array([[ 0.73530097,  0.3553424 ,  0.3719772 ],
>        [ 0.83353373,  0.74622133,  0.14748905],
>        [ 0.72023762,  0.32306969,  0.19142366]])

> >>> unroll(M)
> array([[ 0.        ,  0.        ,  0.73530097],
>        [ 0.        ,  1.        ,  0.3553424 ],
>        [ 1.        ,  1.        ,  0.3719772 ],
>        [ 2.        ,  2.        ,  0.83353373],
>        [ 2.        ,  0.        ,  0.74622133],
>        [ 1.        ,  2.        ,  0.14748905],
>        [ 0.        ,  1.        ,  0.72023762],
>        [ 2.        ,  0.        ,  0.32306969],
>        [ 1.        ,  2.        ,  0.19142366]])


> The docstring sucks. The function is trivial (when you know numpy a bit=
).
> Maybe this function already exists in numpy, if so I couldn't find it.
> Elsewhere I propose it for inclusion.

> Cheers,

> Ga=EBl

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Re: [Numpy-discussion] Helper function to "unroll" a array

[Sven S. <sve...@gm...>]

Gael Varoquaux schrieb:
>     Hi all,
> 
> I didn't get any answers to this email. Is it because the proposed
> addition to numpy is not of any interest to anybody apart from me ?
> Maybe the way I introduced this is wrong. Please tell me what is wrong
> with this proposition.
> 

Well you didn't mentioned why it would be useful for a broad audience,
only that you yourself use it alot. Together with the fact that it's a
one-liner this presumably means that it's not exactly a prime candidate
for adoption. (I'm just another user, so I'm speculating a bit here
based on my reading of past postings on this list.)
-sven

Re: [Numpy-discussion] Helper function to "unroll" a array

[Gael V. <gae...@no...>]

You're probably right. Well it would most definitely be useful for all
the lads in my lab, but I am not sure this is a broad audience. The use
case is when you have a array representing data in an "mgrid" way, and
you wnat to apply transformations to the coordinates. It is something I
have done and seen done quite often.

If I am the only one a the list who see a use for this, then forget it.

Ga=EBl

On Sun, Nov 12, 2006 at 06:07:30PM +0100, Sven Schreiber wrote:
> Well you didn't mentioned why it would be useful for a broad audience,
> only that you yourself use it alot. Together with the fact that it's a
> one-liner this presumably means that it's not exactly a prime candidate
> for adoption. (I'm just another user, so I'm speculating a bit here
> based on my reading of past postings on this list.)