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

[Stefan van der Walt]

On Thu, Mar 22, 2007 at 08:13:22PM -0400, Brian Blais wrote:
> Hello,
> 
> I'd like to concatenate a couple of 1D arrays to make it a 2D array, with two columns
> (one for each of the original 1D arrays).  I thought this would work:
> 
> 
> In [47]:a=arange(0,10,1)
> 
> In [48]:a
> Out[48]:array([0, 1, 2, 3, 4, 5, 6, 7, 8, 9])
> 
> In [49]:b=arange(-10,0,1)
> 
> In [51]:b
> Out[51]:array([-10,  -9,  -8,  -7,  -6,  -5,  -4,  -3,  -2,  -1])
> 
> In [54]:concatenate((a,b))
> Out[54]:
> array([  0,   1,   2,   3,   4,   5,   6,   7,   8,   9, -10,  -9,  -8,
>          -7,  -6,  -5,  -4,  -3,  -2,  -1])
> 
> In [55]:concatenate((a,b),axis=1)
> Out[55]:
> array([  0,   1,   2,   3,   4,   5,   6,   7,   8,   9, -10,  -9,  -8,
>          -7,  -6,  -5,  -4,  -3,  -2,  -1])
> 
> 
> but it never expands the dimensions.  Do I have to do this...
> 
> 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?

How about

N.vstack((a,b)).T

Cheers
Stéfan