Arthimatic and combining in 3D Arrays Numpy

Question

let's say I have a 3D array x:

x = np.arange(0, 24).reshape(4, 3, 2)

output: 
array([[[ 0,  1],
    [ 2,  3],
    [ 4,  5]],

   [[ 6,  7],
    [ 8,  9],
    [10, 11]],

   [[12, 13],
    [14, 15],
    [16, 17]],

   [[18, 19],
    [20, 21],
    [22, 23]]])

If I wanted to concat copies of this row wise, but each time I want to add 1 to the first element of inner each pair, how would I do that?

I can concat 1x

np.concatenate([x, x], axis=0)

And presumably I could do that in a loop (although there may be a better way in Numpy). But the bit I can't figure out is how to +1.

This allows me to add 1 to all the elements, but then I just have a 3x4 matrix of the values +1 and I don't have the rest of the cells!

x[:,:,0] + 1

output:
array([[ 1,  3,  5],
   [ 7,  9, 11],
   [13, 15, 17],
   [19, 21, 23]])

Feels like this is a question that's got to have been asked before? But I can't find enough material on either artithmatic or slicing with multidimensional arrays.

Thank you

Answer 1

Just concatenate and modify:

a = np.concatenate([x, x], axis=0)
a[x.shape[0]:,:,0] += 1