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I want the 3d array to be empty in the beginning and then append an array to index 0 and then append an array to that array.

paths = np.array([], ndmin=3)
print(paths)
print(paths.ndim)

paths = np.append(paths, [])
print(paths)

paths[0] = np.append(paths[0], [3,4,5])
print(paths)

output

[]
3
[]
paths[0] = np.append(paths[0], [3,4,5])
IndexError: index 0 is out of bounds for axis 0 with size 0
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  • 2
    How do you expect the array to look after the operation? Commented Jul 21, 2022 at 18:41
  • What do you mean by the word "add"? Do you mean concatenate, or mathematical addition? Commented Jul 21, 2022 at 18:41
  • 1
    @FCo concatenate / append Commented Jul 21, 2022 at 18:43
  • @DmitriChubarov [ [ [3,4,5] ] ] Commented Jul 21, 2022 at 18:44
  • Do you know the size of the array upfront? It is much faster to allocate memory and then just assign to slices of the array than to concatenate if you're doing it many times, because concatenation requires the entire array to be copied to new memory Commented Jul 21, 2022 at 18:45
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