[Numpy-discussion] Why do mgrid and meshgrid not return broadcast arrays?
warren.weckesser at gmail.com
Wed Mar 8 22:05:21 EST 2017
On Wed, Mar 8, 2017 at 9:48 PM, Juan Nunez-Iglesias <jni.soma at gmail.com>
> I was a bit surprised to discover that both meshgrid nor mgrid return
> fully instantiated arrays, when simple broadcasting (ie with stride=0 for
> other axes) is functionally identical and happens much, much faster.
Take a look at ogrid:
I wrote my own function to do this:
> *def broadcast_mgrid(arrays):*
> * shape = tuple(map(len, arrays))*
> * ndim = len(shape)*
> * result = *
> * for i, arr in enumerate(arrays, start=1):*
> * reshaped = np.broadcast_to(arr[[...] + [np.newaxis] * (ndim -
> * shape)*
> * result.append(reshaped)*
> * return result*
> For even a modest-sized 512 x 512 grid, this version is close to 100x
> *In : %timeit th.broadcast_mgrid((np.arange(512), np.arange(512)))*
> *10000 loops, best of 3: 25.9 µs per loop*
> *In : %timeit np.meshgrid(np.arange(512), np.arange(512))*
> *100 loops, best of 3: 2.02 ms per loop*
> *In : %timeit np.mgrid[:512, :512]*
> *100 loops, best of 3: 4.84 ms per loop*
> Is there a conscious design decision as to why this isn’t what
> meshgrid/mgrid do already? Or would a PR be welcome to do this?
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