CODEWITHSUNDEEP
pythonarrayslistrecursiontree
Vidur Gupta
Vidur Gupta

Reputation: 75

How do I clean a Python list from extraneous nesting?

I am working on a program where we have have a certain list with a lot of extraneous nesting, which we want to simplify.

For example, one input could be 

[[['A', [[[[[[[[[['B', [[[[[[[[[['C', [[[[[[[[[['D']], [['E']], [['F', [[[[[[[[[['G']]]]]]]]]]]], [['H']], [['I']], [['J']]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]

and it should output ['A', ['B', ['C', [['D'], ['E'], ['F', ['G']], ['H'], ['I'], ['J']]]]]

However, after running my code, it is not doing anything and returning [].

Here is my code:

def clean_list(list2):
    for item in list2:
        if isinstance(item, list) and len(list2)==1: # this is an extraneous list!
            item = clean_list(item)
            list2.append(item[0].copy())
            list2.remove(item)
    return list2

Upvotes: 3

Views: 128

Answers (1)

blhsing
blhsing

Reputation: 106768

You can use a function that recursively de-nests each item in the given list, but passes the sub-list to the recursive call if the list has only one item and that item is a list:

def denest(lst):
    if isinstance(lst, list):
        if len(lst) == 1 and isinstance(lst[0], list):
            return denest(lst[0])
        return [denest(i) for i in lst]
    return lst

so that given your sample list stored in variable lst, denest(lst) would return:

['A', ['B', ['C', [['D'], ['E'], ['F', ['G']], ['H'], ['I'], ['J']]]]]

Upvotes: 4

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