sort list of lists in ascending and descending order with strings

Question

I was looking into this question about sorting a list of lists with multiple criteria (element 0 descending and element 1 ascending) .

L = [['a',1], ['a',2], ['a',3], ['b',1], ['b',2], ['b',3]]
L.sort(key=lambda k: (-k[0], k[1]), reverse=True)

is there a way to make it work when the first or the second element is a string?

Python handles string sorting. Have you tried this code? What is the desired output? — inspectorG4dget, Jun 06 '15 at 08:17
I don't see the problem here? The code you give works just fine — Mathieu David, Jun 06 '15 at 08:21

Padraic Cunningham · Answer 1 · 2015-06-06T10:15:38.553

It is simple, just use -ord for your strings:

L.sort(key=lambda k: (-ord(k[0]), k[1]), reverse=True)

Output:

In [1]: L = [['a',1], ['a',2], ['a',3], ['b',1], ['b',2], ['b',3]]

In [2]: L.sort(key=lambda k: (-ord(k[0]), k[1]), reverse=True)

In [3]: L
Out[3]: [['a', 3], ['a', 2], ['a', 1], ['b', 3], ['b', 2], ['b', 1]]

You can get the exact same result by not using reverse and negating the int values:

L = [['a',1], ['a',2], ['a',3], ['b',1], ['b',2], ['b',3]]

L.sort(key=lambda k: (k[0], -k[1]))

print(L)
[['a', 3], ['a', 2], ['a', 1], ['b', 3], ['b', 2], ['b', 1]]

So for a mixture of strings and ints you don't actually need cmp, ord or anything other negating the int values.

score 1 · Answer 2 · answered Jun 06 '15 at 08:43

1

As you want to reverse the sort order for the second string, using the key function won't work. However, using the cmp function will work:

L.sort(cmp=lambda x, y: cmp(x[0], y[0]) or -cmp(x[1], y[1]))

answered Jun 06 '15 at 08:43

llogiq

13,815
8
40
72

I'm not sure I got it. could you modify the example in case element 1 is a string and element 0 is a number? thank you, – Bob Jun 06 '15 at 08:59
cmp no longer exists in python3, there is also no need to use cmp at all – Padraic Cunningham Jun 06 '15 at 10:10
Sorry, I did not see that the question was about python 3.x, I still have 2.7 here. – llogiq Jun 06 '15 at 12:00
@Bob: cmp does not care about type as long as it is innately comparable. So it should not matter if it's a number or string. – llogiq Jun 06 '15 at 12:02

sort list of lists in ascending and descending order with strings

2 Answers2