How to group by arrays to a new array in python

Question

I have some arrays like these:

a1 = [1,2,3,4]
a2 = [6,7,8,9]
a3 = [2,4,6,8]
a4 = ['Mon','Tues']

I want to group them as

result = [
          [[1,6,2,'Mon'],[2,7,4,'Mon']],
          [[3,8,6,'Tues'],[4,9,8,'Tues']]
]

which means if I print the 0th row it will output:

[[1,6,2,'Mon'],[2,7,4,'Mon']]

avloss · Answer 1 · 2020-07-15T14:04:27.880

3

Your a4 is of different length, but otherwise, zip is appropriate function:

>>> a1 = [1,2,3,4]
>>> a2 = [6,7,8,9]
>>> a3 = [2,4,6,8]
>>> a4 = ['Mon','Tues']
>>> a4_long = [item for item in a4 for i in range(len(a1)//len(a4))]
>>>
>>> list(list(l) for l in zip(a1,a2,a3,a4_long))
[
  [1, 6, 2, 'Mon'],
  [2, 7, 4, 'Mon'],
  [3, 8, 6, 'Tues'],
  [4, 9, 8, 'Tues']
]

edited Jul 15 '20 at 14:04

answered Jul 15 '20 at 13:52

avloss

2,389
2
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There are some differences. I expect the a4 should like this:[ [[1,6,2,'Mon'],[2,7,4,'Mon']], [[3,8,6,'Tues'],[4,9,8,'Tues']] ] more specific, [[1,6,2,'Mon'],[2,7,4,'Mon']], two 'Mon's in the same array – YCCLLL Jul 15 '20 at 13:54
Sure, you need to convert tuple into list, if you need that – avloss Jul 15 '20 at 13:56
but two 'Mon's in the different array? – YCCLLL Jul 15 '20 at 13:58
oh, just noticed, let me think – avloss Jul 15 '20 at 14:01

Osadhi Virochana · Answer 2 · 2020-07-15T14:39:28.210

2

This the code for that:

a1 = [1,2,3,4]
a2 = [6,7,8,9]
a3 = [2,4,6,8]
a4 = ['Mon','Tues']
result=[[],[]]
[result[0].append([a1[i],a2[i],a3[i],a4[0]])if i< 2 else result[1].append([a1[i],a2[i],a3[i],a4[1]])for i in range(len(a1))]
print(result)

It outputs:

[[[1, 6, 2, 'Mon'], [2, 7, 4, 'Mon']], [[3, 8, 6, 'Tues'], [4, 9, 8, 'Tues']]]

edited Jul 15 '20 at 14:39

answered Jul 15 '20 at 13:59

Osadhi Virochana

1,294
2
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the output is not what I expect... It should be like this: [[1,6,2,'Mon'],[2,7,4,'Mon']] – YCCLLL Jul 15 '20 at 14:03
I made it, Can you please check? – Osadhi Virochana Jul 15 '20 at 14:40
It's a bad practice and very anti-pythonic [to use list comprehensions for just side effects](https://stackoverflow.com/questions/5753597/is-it-pythonic-to-use-list-comprehensions-for-just-side-effects). – MrNobody33 Jul 15 '20 at 14:43

How to group by arrays to a new array in python

2 Answers2