Sort a list according to the sublists [duplicate]

Question

I am given a list:

lst = [[7090, 1.286], [7486, 2.569], [7571, 0.091]]

I want to sort this list in ascending order according to the second numbers of the sublists (namely, 1.286, 2.569, 0.091) so it looks like [[7571, 0.091], [7090, 1.286], [7486, 2.569]]. How should I do it by using python?

Answer 1

You can do this with Python lists build in sort function.

lst = [[7090, 1.286], [7486, 2.569], [7571, 0.091]]

A typical .sort call would sort it based on the first item per sublist, in ascending order.

lst.sort()
print(lst) # returns [[7090, 1.286], [7486, 2.569], [7571, 0.091]]

To sort it on the second item we can add the following:

lst.sort(key=lambda e: e[1])
print(lst) # returns [[7571, 0.091], [7090, 1.286], [7486, 2.569]]

The key passed to the sort function here takes in each sublist as parameter e and used the second element to sort.

Answer 2

Use the key parameter to sort (or sorted) to specify what you want to sort by.

sorted(lst, key=lambda item: item[1])
# => [[7571, 0.091], [7090, 1.286], [7486, 2.569]]

Alternately, you can use a predefined function from operator — this is equivalent:

from operator import itemgetter
sorted(lst, key=itemgetter(1))