[Numpy-discussion] Axis Iterator?

Tim Hochberg tim.hochberg at ieee.org
Thu Sep 14 20:20:08 CDT 2006


Bill Baxter wrote:
> Iteration over axis 0 is built-in, so you can already do
>     (vectorFunc(row) for row in array)
> And you can use transpose() to make it so the axis you want to iterate
> over is axis 0.
>     (vectorFunc(col) for col in array.transpose(1,0))
> Or just use the .T attribute
>     (vectorFunc(col) for col in array.T)
>
> So it seems kind of a toss-up whether it's worth adding a specific API
> to do that.  The implementation would probably just return the
> transpose with the given axis in the zero slot.   Something like:
>
> def axisiter(arr, i):
>     ax = [i] + range(arr.ndim)
>     del ax[i+1]
>     return arr.transpose(ax)
>
> --bb
>   
Isn't swapaxis appropriate for this? In other words:

for x in arr.swapaxis(0, i):
    #...

should be more or less the same as:

for x in axister(arr, i):
    #....

and it already exists. I'm in a hurry, so I haven't checked the details 
here, but the basic idea seems sound.

-tim

> On 9/15/06, Brendan Simons <brendansimons at yahoo.ca> wrote:
>   
>> Hi all,
>>
>> Just wondering if there was an arbitrary axis iterator in numpy, or
>> if not, if there's demand for one.  What I'm looking for is something
>> which would allow me to do  something like (vectorFunc(column) for
>> column in array.axisIter(1) )  without a bunch of for loops and slicing.
>>
>> Thoughts?
>>     Brendan
>>     
>
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