Questions about shuffling a list in python

Question

What I want to do is to cuts the list in two parts, as evenly sized as possible, then interleaves the elements of the two parts to form the shuffled list. For example, there is a list

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

and I want to rearrange it into

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

I want to change the list in this way. But I have no idea about how to insert all elements into right position.

The algorithm you describe doesn't involve any randomness. Do you actually want to use random.shuffle or do you want to implement what you've said with the cutting and interleaving? — Corentin Pane, Nov 06 '19 at 10:40

Prem Ib · Answer 1 · 2019-11-06T11:00:19.293

1

li, res = [1,2,3,4,5,6,7,8], []
length = len(li)
half = length//2
for i, j in zip(li[:half], li[half:]):
    res.append(i)
    res.append(j)
if length % 2 != 0:
    res.append(li[length - 1])

edited Nov 06 '19 at 11:00

answered Nov 06 '19 at 10:44

Prem Ib

136
2
11

1

`list(chain.from_iterable(zip(...)))` – deceze Nov 06 '19 at 10:45
1

It doesn't work for list with an odd number of items. – Corentin Pane Nov 06 '19 at 10:45
@CorentinPane And what do you expect to happen if the number of items is odd? – Aryerez Nov 06 '19 at 10:47

score 0 · Answer 2 · answered Nov 06 '19 at 10:51

from itertools import chain
my_list = [1, 2, 3, 4, 5, 6, 7, 8]
print(list(chain(*zip(my_list[:len(my_list)//2], my_list[len(my_list)//2:]))) + ([] if len(my_list) % 2 == 0 else [my_list[-1]]))

You didn't specify what you expect if the list has an odd number of items, so I assumed you want to append the remaining item at the end of the final list.

score 0 · Answer 3 · answered Nov 06 '19 at 11:11

Here's a simpler one:

from math import ceil
my_list = [1,2,3,4,5,6]

result = sum([my_list[i::ceil(len(my_list)/2)] for i in range(ceil(len(my_list)/2))],[])

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

my_list = [1,2,3,4,5,6,7]

result = sum([my_list[i::ceil(len(my_list)/2)] for i in range(ceil(len(my_list)/2))],[])

# [1, 5, 2, 6, 3, 7, 4]

Questions about shuffling a list in python

3 Answers3