How do I concatenate subarrays of a list into one list; ie create a flat list?

Question

Assume I have array arr = [[1, 2, 3], [4, 5, 6]]

How do I concatenate this array into one array, such as arr = [1, 2, 3, 4, 5, 6]

Thanks in advance!

Does this answer your question? [How do I concatenate two lists in Python?](https://stackoverflow.com/questions/1720421/how-do-i-concatenate-two-lists-in-python) — Rivers, Aug 15 '21 at 17:23

score 1 · Answer 1 · answered Aug 15 '21 at 17:22

1

The most basic approach will be a double loop list comprehension

arr = [[1, 2, 3], [4, 5, 6]]
print([j for i in arr for j in i])

alternatively

arr = [[1, 2, 3], [4, 5, 6]]
print(sum(arr,start = []))

answered Aug 15 '21 at 17:22

Oreo

score 0 · Answer 2 · answered Aug 15 '21 at 17:19

0

You can use itertools

import itertools
arr = [[1, 2, 3], [4, 5, 6]]
arr2=list(itertools.chain.from_iterable(arr))

answered Aug 15 '21 at 17:19

score 0 · Accepted Answer · answered Aug 15 '21 at 17:20

0

Try this:

arr = [[1, 2, 3], [4, 5, 6]]
arr2 = []
for x in arr:
  arr2+= x

Result:

[1, 2, 3, 4, 5, 6]

answered Aug 15 '21 at 17:20

RatajS

3 Answers3