flatten an irregular list and reshape another same-lenght flat list reconstructuning the original element order

Question

Take an irregularly shaped list such as:

L = [[[1,2,3],[4,5],6]

(by irregularly shaped I mean whatever irregular shape, not just the irregular one I used as example). Now make it flat as described here obtaining

L_flat = [1,2,3,4,5,6]

Take now a new list with the same shape of the flat one such as:

L_flat_new = [a,b,c,d,e,f]

how can I reconstruct this new list to have the same shape of the original one element-wise?

desired output: L_flat_new_reshaped = [[[a,b,c],[d,e],f]

here's [an entry](https://stackoverflow.com/q/50554603/849891) asking for the exactly same thing, with answers in JS, Scala, and Scheme (and some pseudocode). — Will Ness, Aug 16 '22 at 13:41

score 4 · Accepted Answer · answered Aug 16 '22 at 11:27

4

Try recursion:

L = [[[1, 2, 3], [4, 5], 6]]

L_flat_new = ["a", "b", "c", "d", "e", "f"]


def reshape(orig, i):
    if isinstance(orig, list):
        return [reshape(v, i) for v in orig]
    else:
        return next(i)


print(reshape(L, iter(L_flat_new)))

Prints:

[[['a', 'b', 'c'], ['d', 'e'], 'f']]

answered Aug 16 '22 at 11:27

Andrej Kesely

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Maybe try another List - ```reshape([[1, 2], [3, 4], [5, 6]], L_flat_new)``` - it will not work?! – Daniel Hao Aug 16 '22 at 13:54
2

@DanielHao Yes. Just put `iter()` on the second parameter: `print(reshape([[1, 2], [3, 4], [5, 6]], iter(L_flat_new)))` – Andrej Kesely Aug 16 '22 at 14:05

flatten an irregular list and reshape another same-lenght flat list reconstructuning the original element order

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