Sorting A Tuple Of Strings Alphabetically And Reverse Alaphabetically'

Lets say you have a list of tuples (last_name, first_name) and you want to sort them reverse alphabetically by last_name and then if two people have the same name for them to be so

Solution 1:

Is there a way to do this with one line?

With two lines I guess you could rely on sort stability and first sort by first name and then sort by last name reversed.

Well you can do exactly that in one line:

sorted(sorted(names, key=lambda name: name[1]), key=lambda name: name[0], reverse=True)

Doing two sorts for exactly this problem in the Sorting Mini-HOW TO ("to sort the student data by descending grade and then ascending age, do the age sort first and then sort again using grade").

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A silly alternative doing it with just one sorted and key:

sorted(names, key=lambda name: ([-ord(c) for c in name[0]], name[1])) == correct

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A Python 2 solution with one sorted and cmp instead of key:

sorted(names, lambda a, b: cmp(b[0], a[0]) or cmp(a, b))

Solution 2:

Here's an itertools.groupby solution:

from itertools import groupby
from operator import itemgetter

li = [('x', 'y'), ('s', 'e'), ('s', 'a'), ('x', 'z')]

[p for k, g in groupby(sorted(li, reverse=True), itemgetter(0)) for p inreversed(list(g))]
# [('x', 'y'), ('x', 'z'), ('s', 'a'), ('s', 'e')]

Solution 3:

Yes, you can rely on the stability of the sorting:

names = [('Zane', 'Albert'), ('Zane', 'Bart'), ('Python', 'Alex'), ('Python', 'Monty')]

names.sort()
names.sort(reverse=True, key=lambda i: i[0])