Turning a list into nested lists in python

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How can I turn a list into an array in python?

How can I turn a list such as:

data_list = [0,1,2,3,4,5,6,7,8]

into a list of lists such as:

new_list = [ [0,1,2] , [3,4,5] , [6,7,8] ]

ie I want to group ordered elements in a list and keep them in an ordered list. How can I do this?

Thanks

list nested python
8 Answers

Based on the answer from Fred Foo, if you're already using numpy, you may use reshape to get a 2d array without copying the data:

import numpy
new_list = numpy.array(data_list).reshape(-1, 3)
user_10335810

The following function expands the original context to include any desired list of lists structure:

def gen_list_of_lists(original_list, new_structure):
    assert len(original_list) == sum(new_structure), \
    "The number of elements in the original list and desired structure don't match"
        
    list_of_lists = [[original_list[i + sum(new_structure[:j])] for i in range(new_structure[j])] \
                     for j in range(len(new_structure))]
        
    return list_of_lists

Using the above:

data_list = [0,1,2,3,4,5,6,7,8]
    
new_list = gen_list_of_lists(original_list=data_list, new_structure=[3,3,3])
# The original desired outcome of [[0,1,2], [3,4,5], [6,7,8]]

new_list = gen_list_of_lists(original_list=data_list, new_structure=[2,3,3,1])
# [[0, 1], [2, 3, 4], [5, 6, 7], [8]]
Admin1

The below one is more optimized and quite straightforward.

data_list = [0,1,2,3,4,5,6,7,8]
result =[]
i=0
while i <(len(data_list)-2):
    result.append(data_list[i:i+3])
    i+=3
print(result)

**output**

[[0, 1, 2], [3, 4, 5], [6, 7, 8]]

user_105795530
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