Combining numpy multi-dimensional arrays

Question

Im facing a little issue to combine arrays in a certain manner. Let's say we have

a=array([[1,1,1],[2,2,2],[3,3,3]])

b=array([[10,10,10],[20,20,20],[30,30,30]])

I wish to get

c=array([[[1,1,1],[10,10,10]],[[2,2,2],[20,20,20]],[[3,3,3],[30,30,30]]])

The real issue is that my arrays a and b are much longer than 3 coordinates!

The best I achieved using concatenate is:

concatenate((a,b),axis=2)

which results in

array([[ 1, 1, 1, 10, 10, 10], [ 2, 2, 2, 20, 20, 20], [ 3, 3, 3, 30, 30, 30]])

it is pretty good but not have enough depth.

Also, I've tried something from another question to get the desired depth:

d=concatenate((a[...,None],b[...,None]),axis=2)

but results in:

 array([[[ 1, 10],
    [ 1, 10],
    [ 1, 10]],

   [[ 2, 20],
    [ 2, 20],
    [ 2, 20]],

   [[ 3, 30],
    [ 3, 30],
    [ 3, 30]]])

Which still does not works...

Answer 1

ummm zip(a,b) ?

is not what you want??

>>> a=array([[1,1,1],[2,2,2],[3,3,3]]);b=array([[10,10,10],[20,20,20],[30,30,30]
>>> zip(a,b)
[(array([1, 1, 1]), array([10, 10, 10])), (array([2, 2, 2]), array([20, 20, 20])), (array([3, 3, 3]), array([30, 30, 30]))]

Answer 2

It seems like you want to add a new axis between 0 and 1 so put the None in the middle. This will shift axis 1 be axis 2 and create a new dimension at 1. Like so:

a = array([[1,1,1],[2,2,2],[3,3,3]])
b = array([[10,10,10],[20,20,20],[30,30,30]])
c = concatenate((a[:, None, :], b[:, None, :]), axis=1)

>>> c
array([[[ 1,  1,  1],
    [10, 10, 10]],

   [[ 2,  2,  2],
    [20, 20, 20]],

   [[ 3,  3,  3],
    [30, 30, 30]]])

Answer 3

You're looking for numpy.stack . It's used for joining arrays along a new axis; in contrast to 'numpy.concatenate', which is for joining arrays along an existing axis. With stack , you specify the axis to join along in terms of which axis it would be after the stacking; so you would specify axis 1.

a = array([[1,1,1],[2,2,2],[3,3,3]])
b = array([[10,10,10],[20,20,20],[30,30,30]])
c = stack((a, b), axis=1)

>>> c
array([[[ 1,  1,  1],
    [10, 10, 10]],

   [[ 2,  2,  2],
    [20, 20, 20]],

   [[ 3,  3,  3],
    [30, 30, 30]]])