Hi I need a single list of nested lists in python without any inbuilt function. I did a lot of research but not able to find without flatten or ravel function().
for ex:
input = [1,2,[2,3,[4,5]],[6,7],[8,[9]],10]
output = [1,2,2,3,4,5,6,7,8,9,10]
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eyllanesc
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pooja dudy
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[The first solution here](https://stackoverflow.com/questions/952914/how-to-make-a-flat-list-out-of-list-of-lists) doesn't use any built-in functions. Is this acceptable? – DarrylG Nov 03 '19 at 16:34
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You can use recursion to implement your own `flatten` function. – Rithin Chalumuri Nov 03 '19 at 16:34
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@DarrylG This was not working – pooja dudy Nov 03 '19 at 16:39
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duplicate of https://stackoverflow.com/questions/2158395/flatten-an-irregular-list-of-lists – actual_panda Nov 03 '19 at 16:46
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You're right, that only works when all elements are lists. – DarrylG Nov 03 '19 at 17:26
2 Answers
1
You can use recursion to implement your own flatten function. Here's a nice tutorial explaining the concepts of recursion.
The idea here is that you loop through each element in your list and if you encounter a sublist you recursively call the same method with the current list. If it's a valid element you add it to to your output list.
Example:
def flatten(input_list, output_list=[]):
for i in input_list:
if isinstance(i, list):
flatten(i, output_list)
else:
output_list.append(i)
return output_list
input_list = [1,2,[2,3,[4,5]],[6,7],[8,[9]],10]
print(flatten(input_list))
Outputs:
[1, 2, 2, 3, 4, 5, 6, 7, 8, 9, 10]
Rithin Chalumuri
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Would suggest changing function signature to: def flatten(input_list, output_list = []). That way the user does not have to create or pass output on call. – DarrylG Nov 03 '19 at 17:47
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0
I found a solution on my own. Below is the solution:
c = []
def test(a):
for val in a:
if type(val) == list:
test(val)
else:
c.append(val)
return c
a=[1,2,[2,3,[4,5]],[6,7],[8,[9]],10] print test(a)
pooja dudy
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