[Numpy-discussion] concatenating 1-D arrays to 2D

Stefan van der Walt stefan@sun.ac...
Fri Mar 23 11:23:53 CDT 2007


On Fri, Mar 23, 2007 at 11:09:03AM -0400, Robert Pyle wrote:
> > In [65]:concatenate((a.reshape(10,1),b.reshape(10,1)),axis=1)
> > Out[65]:
> > array([[  0, -10],
> >         [  1,  -9],
> >         [  2,  -8],
> >         [  3,  -7],
> >         [  4,  -6],
> >         [  5,  -5],
> >         [  6,  -4],
> >         [  7,  -3],
> >         [  8,  -2],
> >         [  9,  -1]])
> >
> >
> > ?
> >
> > I thought there would be an easier way.  Did I overlook something?
> 
> What's wrong with zip? Or did *I* miss the point?  (I'm just getting  
> the hang of numpy.)

If you use 'zip' you don't make use of numpy's fast array mechanisms.
I attach some code you can run as a benchmark.  From my ipython
session:

In [1]: run vsbench.py

In [2]: timeit using_vstack(x,y)
1000 loops, best of 3: 997 µs per loop

In [3]: timeit using_zip(x,y)
10 loops, best of 3: 503 ms per loop

In [4]: timeit using_custom_iteration(x,y)
1000 loops, best of 3: 1.64 ms per loop

Cheers
Stéfan
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