How to sort a list/tuple of lists/tuples by the element at a given index?

I have some data either in a list of lists or a list of tuples, like this:

data = [[1,2,3], [4,5,6], [7,8,9]]
data = [(1,2,3), (4,5,6), (7,8,9)]

And I want to sort by the 2nd element in the subset. Meaning, sorting by 2,5,8 where 2 is from (1,2,3), 5 is from (4,5,6). What is the common way to do this? Should I store tuples or lists in my list?

Solution 1:

sorted_by_second = sorted(data, key=lambda tup: tup[1])

or:

data.sort(key=lambda tup: tup[1])  # sorts in place

The default sort mode is ascending. To sort in descending order use the option reverse=True:

sorted_by_second = sorted(data, key=lambda tup: tup[1], reverse=True)

or:

data.sort(key=lambda tup: tup[1], reverse=True)  # sorts in place

Solution 2:

from operator import itemgetter
data.sort(key=itemgetter(1))

Solution 3:

For sorting by multiple criteria, namely for instance by the second and third elements in a tuple, let

data = [(1,2,3),(1,2,1),(1,1,4)]

and so define a lambda that returns a tuple that describes priority, for instance

sorted(data, key=lambda tup: (tup[1],tup[2]) )
[(1, 1, 4), (1, 2, 1), (1, 2, 3)]