Concatenate two numpy arrays together index-wise

Question

I have two 2D numpy arrays:

a = np.array([[0,1,2,3,4],
              [0,1,2,3,4],
              [0,1,2,3,4]
              ...
              ])

b = np.array([[0,0,0,0,0],
              [1,1,1,1,1],
              [2,2,2,2,2],
              ...
              ])

How would I be able to get a numpy array where each exact index will concatenate together?

OUT:
[[0,0], [1,0], [2,0], [3,0], [4,0] [0,1], [1,1], [2,1], [3,1], [4,1] ...]

The two sample arrays don't have the same shape. How do you expect to pair them index-wise? That is, what do you do with un-aligned indexes? — Quang Hoang
– Quang Hoang, Commented Feb 25, 2021 at 16:02
Apologies, you are right, I did not write the input correctly Edit: I have made the two sample arrays of the same shape - the initial question stays the same! — D.Kang
– D.Kang, Commented Feb 25, 2021 at 16:04

Kenan · Accepted Answer · 2021-02-25 16:14:17Z

2

You want stack

result = np.stack((a,b), axis=2)
array([[[0, 0],
        [1, 0],
        [2, 0],
        [3, 0],
        [4, 0]],

       [[0, 1],
        [1, 1],
        [2, 1],
        [3, 1],
        [4, 1]],

       [[0, 2],
        [1, 2],
        [2, 2],
        [3, 2],
        [4, 2]]])

Taken from @user15270287, you can reshape the results with np.reshape(result, (-1, 2))

edited Feb 25, 2021 at 16:14

answered Feb 25, 2021 at 16:11

Kenan

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1 Comment

user15270287 Over a year ago

To get a 2d array like you want you can do np.reshape(result, (-1, 2)) after this

Sayandip Dutta · Accepted Answer · 2021-02-25 16:11:17Z

2

You can use np.dstack:

>>> a = np.array([[0,1,2,3,4],
              [0,1,2,3,4],
              [0,1,2,3,4]
              ])

>>> b = np.array([[0,0,0,0,0],
              [1,1,1,1,1],
              [2,2,2,2,2],
              ])

>>> np.dstack((a, b)).reshape(-1, 2)
array([[0, 0],
       [1, 0],
       [2, 0],
       [3, 0],
       [4, 0],
       [0, 1],
       [1, 1],
       [2, 1],
       [3, 1],
       [4, 1],
       [0, 2],
       [1, 2],
       [2, 2],
       [3, 2],
       [4, 2]])

answered Feb 25, 2021 at 16:11

Sayandip Dutta

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Comments

Manoj Hegde · Accepted Answer · 2021-02-25 16:40:27Z

0

def mapper(x):
    temp = []
    for a,b in zip(x[0],x[1]):
        temp.append([a,b])
    return temp

result = list(map(lambda x:mapper(x),zip(a,b)))

Output:

[[[0, 0], [1, 0], [2, 0], [3, 0], [4, 0]],
 [[0, 1], [1, 1], [2, 1], [3, 1], [4, 1]],
 [[0, 2], [1, 2], [2, 2], [3, 2], [4, 2]]]

answered Feb 25, 2021 at 16:40

Manoj Hegde

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