CODEWITHSUNDEEP
pythonarrayssortingmatrixmultidimensional-array
JacksonFreeman
JacksonFreeman

Reputation: 33

How to paste 2D Arrays onto each other

I'm trying to simply stack two 2D arrays onto each other like this, if I have two 2D arrays like this:

a = [[0, 0],
   [0, 0]]
b = [[1, 1],
   [1, 1]]

I want this output:

ab = [['01', '01'],
     ['01', '01']]

It is important that the final array elements (e.g. 01) are one string and not seperate elements(like ['0','1']). I've been trying with zip and dstack but cannot get it right.

Edit: I didn't mention this in the OP but the output matrix should also have the same dimensions NxN dimensions as the 2 input matrices.

Upvotes: 0

Views: 131

Answers (4)

shomeax
shomeax

Reputation: 865

That's actually quite an interesting question if array dimensions are quite large.

You can try dstack+apply_along_axis approach. Here, dstack would sandwich two your arrays atop each other, and apply_along_axis(.. , 2, ..) would apply a conversion function to each 1x1x2 canapé of that sandwich.

The trick is to provide conversion function, here I propose "convert to int, convert to string and join strings" as a simple nested lambda.

import numpy as np

np.apply_along_axis(lambda x: ''.join(map(lambda y:str(int(y)),x)), 2, np.dstack((np.array(a),np.array(b))))

>>> a = np.zeros((10,10))
>>> a
array([[0., 0., 0., 0., 0., 0., 0., 0., 0., 0.],
       [0., 0., 0., 0., 0., 0., 0., 0., 0., 0.],
       [0., 0., 0., 0., 0., 0., 0., 0., 0., 0.],
       [0., 0., 0., 0., 0., 0., 0., 0., 0., 0.],
       [0., 0., 0., 0., 0., 0., 0., 0., 0., 0.],
       [0., 0., 0., 0., 0., 0., 0., 0., 0., 0.],
       [0., 0., 0., 0., 0., 0., 0., 0., 0., 0.],
       [0., 0., 0., 0., 0., 0., 0., 0., 0., 0.],
       [0., 0., 0., 0., 0., 0., 0., 0., 0., 0.],
       [0., 0., 0., 0., 0., 0., 0., 0., 0., 0.]])
>>> b = np.ones((10,10))
>>> b
array([[1., 1., 1., 1., 1., 1., 1., 1., 1., 1.],
       [1., 1., 1., 1., 1., 1., 1., 1., 1., 1.],
       [1., 1., 1., 1., 1., 1., 1., 1., 1., 1.],
       [1., 1., 1., 1., 1., 1., 1., 1., 1., 1.],
       [1., 1., 1., 1., 1., 1., 1., 1., 1., 1.],
       [1., 1., 1., 1., 1., 1., 1., 1., 1., 1.],
       [1., 1., 1., 1., 1., 1., 1., 1., 1., 1.],
       [1., 1., 1., 1., 1., 1., 1., 1., 1., 1.],
       [1., 1., 1., 1., 1., 1., 1., 1., 1., 1.],
       [1., 1., 1., 1., 1., 1., 1., 1., 1., 1.]])

>>> np.apply_along_axis(lambda x: ''.join(map(lambda y:str(int(y)),x)), 2, np.dstack((a,b)))
array([['01', '01', '01', '01', '01', '01', '01', '01', '01', '01'],
       ['01', '01', '01', '01', '01', '01', '01', '01', '01', '01'],
       ['01', '01', '01', '01', '01', '01', '01', '01', '01', '01'],
       ['01', '01', '01', '01', '01', '01', '01', '01', '01', '01'],
       ['01', '01', '01', '01', '01', '01', '01', '01', '01', '01'],
       ['01', '01', '01', '01', '01', '01', '01', '01', '01', '01'],
       ['01', '01', '01', '01', '01', '01', '01', '01', '01', '01'],
       ['01', '01', '01', '01', '01', '01', '01', '01', '01', '01'],
       ['01', '01', '01', '01', '01', '01', '01', '01', '01', '01'],
       ['01', '01', '01', '01', '01', '01', '01', '01', '01', '01']],
      dtype='<U2')

Upvotes: 1

user2261062
user2261062

Reputation:

You can do this in a double comprehension list

Edit: Added an int cast to make sure the values don't get interpreted as floats

a = [[0, 0], [0, 0]]
b = [[1, 1], [1, 1]]

result = [[str(int(i)) + str(int(j))] for c,d in zip(a,b) for i,j in zip(c,d)]
result = [[result[0][0], result[1][0]], [result[2][0], result[3][0]]]
print result

[['01', '01'], ['01', '01']]

Upvotes: 1

Dhana D.
Dhana D.

Reputation: 1720

If both 2D arrays always have same size m*n, you can try using this basic nested-looping:

a = [[0, 0],
   [0, 0]]
b = [[1, 1],
   [1, 1]]
c = []
for i in range(len(a)):
    temp = []
    for j in range(len(a[i])):
        temp.append(str(a[i][j])+str(b[i][j]))
    c.append(temp)

Upvotes: 0

Achille G
Achille G

Reputation: 817

you can try the following if you want the result as strings, otherwise remove the str method

c = [[str(x[0]) + str(y[0]), str(x[1]) + str(y[1])] for x, y in list(zip(a, b))]

Upvotes: 0

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