Python: Iterating lists with different amount of dimensions, is there a generic way?

Question

# 2x3 dimensional list
multidim_list = [ 
                  [1,2,3],
                  [4,5,6],    
                ]
# 2x3x2 dimensional list
multidim_list2 = [ 
                   [ 
                     [1,2,3],
                     [4,5,6],  
                   ],
                   [ 
                     [7,8,9],
                     [10,11,12],  
                   ]
                 ]

def multiply_list(list):
    ...

I would like to implement a function, that would multiply all elements in list by two. However my problem is that lists can have different amount of dimensions.

Is there a general way to loop/iterate multidimensional list and for example multiply each value by two?

EDIT1:
Thanks for the fast answers.
For this case, I don’t want to use numpy.
The recursion seems good, and it doesn’t even need to make copy of the list, which could be quite large actually.

Asked By: JoonasS

||

Source

Answer 1

Recursion is your friend:

from collections import MutableSequence
def multiply(list_):
    for index, item in enumerate(list_):
        if isinstance(item, MutableSequence):
            multiply(item)
        else:
            list_[index] *= 2

You could just do isinstance(item, list) instead of isinstance(item, MutableSequence), but the latter way is more futureproof and generic. See the glossary for a short explanation.

Answered By: Lauritz V. Thaulow

Answer 2

numpy arrays do that out of the box.

Answered By: Roland Smith

Answer 3

You can make use of numpy:

import numpy as np

arr_1 = np.array(multidim_list)
arr_2 = np.array(multidim_list2)

Result:

>>> arr_1*2
array([[ 2,  4,  6],
       [ 8, 10, 12]])
>>> arr_2*2
array([[[ 2,  4,  6],
        [ 8, 10, 12]],

       [[14, 16, 18],
        [20, 22, 24]]])

Answered By: Akavall

Python: Iterating lists with different amount of dimensions, is there a generic way?

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