Sort a list by multiple attributes?


Question

I have a list of lists:

[[12, 'tall', 'blue', 1],
[2, 'short', 'red', 9],
[4, 'tall', 'blue', 13]]

If I wanted to sort by one element, say the tall/short element, I could do it via s = sorted(s, key = itemgetter(1)).

If I wanted to sort by both tall/short and colour, I could do the sort twice, once for each element, but is there a quicker way?

1
373
10/20/2016 11:06:47 AM

Accepted Answer

A key can be a function that returns a tuple:

s = sorted(s, key = lambda x: (x[1], x[2]))

Or you can achieve the same using itemgetter (which is faster and avoids a Python function call):

import operator
s = sorted(s, key = operator.itemgetter(1, 2))

And notice that here you can use sort instead of using sorted and then reassigning:

s.sort(key = operator.itemgetter(1, 2))
627
4/24/2018 10:05:22 PM

I'm not sure if this is the most pythonic method ... I had a list of tuples that needed sorting 1st by descending integer values and 2nd alphabetically. This required reversing the integer sort but not the alphabetical sort. Here was my solution: (on the fly in an exam btw, I was not even aware you could 'nest' sorted functions)

a = [('Al', 2),('Bill', 1),('Carol', 2), ('Abel', 3), ('Zeke', 2), ('Chris', 1)]  
b = sorted(sorted(a, key = lambda x : x[0]), key = lambda x : x[1], reverse = True)  
print(b)  
[('Abel', 3), ('Al', 2), ('Carol', 2), ('Zeke', 2), ('Bill', 1), ('Chris', 1)]

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