Loop through 3d array and add 2d slices N times

Question

I have a 3d array (lets name it a) with shape = (365, 28, 36). I consider this array as an 3d array with 365 pieces of 2d arrays (28,36) stacked on each other. I want now to loop through this 3d array and each 2d slice should be repeated 8 times and then stacked on each other. This means that I will end up with one array of size (2920, 28, 36). 2920 comes from 365*8.

My attempt so far has been this, but it does not work. Can anyone help with this problem?

l = []
for i in range(365):
    for j in range(28):
        for k in range(30):  
            l.extend(repeat(a[i,j,k], 8))

Answer 1

newarray = []
for arr2d in oldarray:
    for _ in range(8):
        newarray.append(arr2d)

Arrays in python are actually lists, which mean they are variable length, so you can just do this. oldarray is your old 3d array, newarray is your desired output, and arr2d is the 2d array inside oldarray.

Answer 2

You have several syntax errors in your code. Also, I suspect that you want eight independent copies of the 2D data, rather than 8 pointers to the 2D slice (where if you change one value, you change them all).

Try this:

from copy import deepcopy

a = [
     [[1, 2, 3], ['a', 'b', 'c']],
     [[4, 5, 6], ['@', '#', '$']],
     [[7, 8, 9], ['X', 'Y', 'Z']]
    ]

l = []
for slice in a:
    l.extend([deepcopy(slice) for _ in range(8)])

l[0][0][0] = "FLAG"
print l

IN the final print, note how only one location changes to the string "FLAG", rather than all 8 copies of that slice changing.