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Create a flat list out of a list of lists in Python

Let’s take a list of lists.

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list2d = [[1,2,3], [4,5,6], [7], [8,9]]

To merge this lists to a flat list you can use the following ways.

itertools.chain()

import itertools

list2d = [[1,2,3], [4,5,6], [7], [8,9]]
merged = list(itertools.chain(*list2d))
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functools.reduce()

from functools import reduce
list2d = [[1,2,3], [4,5,6], [7], [8,9]]
reduce(lambda x, y: x+y, list2d)
#[1, 2, 3, 4, 5, 6, 7, 8, 9]

list.extend()

list2d = [[1,2,3], [4,5,6], [7], [8,9]]
out = []
for sublist in list2d:
    out.extend(sublist)
See also  TypeError: 'str' object does not support item assignment - Python error - How to fix?

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