Sorting by list column

Question

I have this list like this:

list1 = [["A",5,2,8,3],["B",9,5,1,5]]

And I'm trying to sort it by the second column. I would expect list1 to then be

[["B",9,5,1,5],["A",5,2,8,3]]

Because 9 is greater than 5 right? I'm using

sorted(lis1, key=lambda a : a[1])

however it doesn't sort it; it just remains as it was before. Why isn't this working?

It sorts in ascending order by default. Add the argument `reverse=True` to your `sorted` function to generate the desired output — gtlambert, Feb 29 '16 at 21:13

score 2 · Answer 1 · answered Feb 29 '16 at 21:21

2

sorted:

Return a new sorted list from the items in iterable

It does not sort in place.

answered Feb 29 '16 at 21:21

score 1 · Answer 2 · answered Feb 29 '16 at 21:13

1

You just need to reverse it:

list1 = [["A",5,2,8,3],["B",9,5,1,5]]
list1 = sorted(list1, key=lambda a : a[1], reverse=True)
print(list1)
# outputs [["B",9,5,1,5],["A",5,2,8,3]]

9>5, so it comes afterwards, unless you reverse.

answered Feb 29 '16 at 21:13

rofls

4,993
3
27
37

Tried that and it still has not changed.. – Alster Feb 29 '16 at 21:16
Strange... when I copy the above code and run it it works – rofls Feb 29 '16 at 21:16
1

Are you sure you're doing: `list1 = sorted(list1, key=lambda a : a[1], reverse=True)`? `sorted` doesn't modify the list, it returns a modified list... – rofls Feb 29 '16 at 21:17
You can also do: `list1.sort(key=lambda a : a[1], reverse=True)` and it will modify `list1` so that you don't need to reassign to it. – rofls Feb 29 '16 at 21:18
1

Ahah! Yes that works now I added list1 = before it. Thanks! – Alster Feb 29 '16 at 21:19

score 0 · Answer 3 · answered Feb 29 '16 at 21:42

using operator.itemgetter() function:

from operator import itemgetter

list1 = [["A",5,2,8,3],["B",9,5,1,5],["C",1,2,8,3]]

print(sorted(list1, key=itemgetter(1)))
print(sorted(list1, key=itemgetter(1), reverse=True))

Output:

[['C', 1, 2, 8, 3], ['A', 5, 2, 8, 3], ['B', 9, 5, 1, 5]]
[['B', 9, 5, 1, 5], ['A', 5, 2, 8, 3], ['C', 1, 2, 8, 3]]

Sorting by list column

3 Answers3