CODEWITHSUNDEEP
pythonlistrecursionmultidimensional-array
VirusFreeNewt
VirusFreeNewt

Reputation: 27

How to create a multidimensional list of a variable amount of dimensions in python?

I am trying to create a function that will make a multidimensional list taking an input number to choose the amount of dimensions the list will be. This is my code so far:

def createMultiDimList(dimensions, currentDim=0, output=[]):
    if currentDim < dimensions:
        output.append([])
        currentDim += 1
        createMultiDimList(dimensions, currentDim, output[0])
        return output
    else:
        return output

I think this isn't working because the recursion is just putting in the single dimensional list, but I am not sure on that.

Upvotes: 0

Views: 351

Answers (2)

Samwise
Samwise

Reputation: 71562

You're overcomplicating it IMO. The general idea behind recursion is to solve the easiest case first, and then return the result of the more difficult case in terms of an incrementally easier case.

For this function, the "easy case" is that a 1-dimensional list is []. The incrementally easier case is that an n-dimensional list is an n-1-dimensional list inside a list. Hence:

>>> def n_dim_list(n: int) -> list:
...     if n == 1:
...         return []
...     return [n_dim_list(n-1)]
...
>>> n_dim_list(4)
[[[[]]]]

If you wanted to complicate it a bit to make it a more interesting example of recursion, you could define a filler value for the 1-dimensional lists and the length of each list:

>>> def n_dim_list(n: int, length: int = 0, value = None) -> list:
...     if n == 1:
...         return [value] * length
...     return [n_dim_list(n-1, length, value) for _ in range(length or 1)]
...
>>> n_dim_list(4)
[[[[]]]]
>>> n_dim_list(4, 2, 0)
[[[[0, 0], [0, 0]], [[0, 0], [0, 0]]], [[[0, 0], [0, 0]], [[0, 0], [0, 0]]]]

Upvotes: 3

adir abargil
adir abargil

Reputation: 5745

as @Samwise wisely said, you have simpled awesome approuch like his, specifically for your issue, you need to send down nested list instead of appending item and returning it:

def createMultiDimList(dimensions, currentDim=0, output=[]):
    if currentDim < dimensions:
        currentDim += 1
        createMultiDimList(dimensions, currentDim, [output])
        return output
    else:
        return output

Upvotes: 1

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