Python: Sorting by Second Element

Question

I'm trying to sort these coordinates by the first element and the second element. The first element are just simple alphabets, and the second element are numerical values.

I found out how to make the program print by the first element - by alphabetical order. Which works - but I'm having difficulties with attempting to solve it by the numerical values.

How would this problem be apporached?

coor_tuples = [
                ('f', 9),
                ('z,', 2),
                ('t', 4),
                ('x', 8),
                ('b', 1),
                ('m', 7)
]

sorted(coor_tuples, key=lambda coor: coor[1])

print(coor_tuples)

Please repeat [on topic](https://stackoverflow.com/help/on-topic) and [how to ask](https://stackoverflow.com/help/how-to-ask) from the [intro tour](https://stackoverflow.com/tour). In particular, we need you to specify what you're trying to do; include an example or two. Give us the expected [minimal, reproducible example](https://stackoverflow.com/help/minimal-reproducible-example), so we can see exactly where you need help. — Prune, Sep 25 '20 at 04:02
`sorted` doesn't work in place, you need to assign the output... — Nick, Sep 25 '20 at 04:03
Also, make sure that you have consulted applicable tutorials on sorting. — Prune, Sep 25 '20 at 04:03
Does this answer your question? [What is the difference between \`sorted(list)\` vs \`list.sort()\`?](https://stackoverflow.com/questions/22442378/what-is-the-difference-between-sortedlist-vs-list-sort) — Nick, Sep 25 '20 at 04:04

score 0 · Answer 1 · answered Sep 25 '20 at 04:03

The problem is that the sorted function returns the sorted array, leaving the original array intact, instead of sorting the array you put in. You should try

coor_tuples = [
                ('f', 9),
                ('z,', 2),
                ('t', 4),
                ('x', 8),
                ('b', 1),
                ('m', 7)
]

coor_tuples=sorted(coor_tuples, key=lambda coor: coor[1])

print(coor_tuples)

score 0 · Answer 2 · answered Sep 25 '20 at 04:03

The sorted method returns a sorted collection. You need to set it.

coor_tuples = [
                ('f', 9),
                ('z,', 2),
                ('t', 4),
                ('x', 8),
                ('b', 1),
                ('m', 7)
]

coor_tuples = sorted(coor_tuples, key=lambda coor: coor[1])  # update collection

print(coor_tuples)

Output

[('b', 1), ('z,', 2), ('t', 4), ('m', 7), ('x', 8), ('f', 9)]

score 0 · Answer 3 · answered Sep 25 '20 at 04:03

You forgot to assign back to coor_tuples, so the result of sorted is discarded. Either assign back:

coor_tuples = sorted(coor_tuples, key=lambda coor: coor[1])

or use the .sort method instead, to sort in place:

coor_tuples.sort(key=lambda coor: coor[1])

I'd recommend the latter in this case, since it's already a list; unless you need the original unsorted data, there's no reason not to sort in place and save unnecessary temporaries.

Python: Sorting by Second Element

3 Answers3