按每个子列表的第一个元素对列表列表进行排序

Question

How to sort a list of lists according to the first element of each list?

For example, giving this unsorted list:

[[1,4,7],[3,6,9],[2,59,8]]

The sorted result should be:

[[1,4,7],[2,59,8],[3,6,9]]

Answer 1

Use sorted function along with passing anonymous function as value to the key argument. key=lambda x: x[0] will do sorting according to the first element in each sublist.

>>> lis = [[1,4,7],[3,6,9],[2,59,8]]
>>> sorted(lis, key=lambda x: x[0])
[[1, 4, 7], [2, 59, 8], [3, 6, 9]]

Answer 2

If you're sorting by first element of nested list, you can simply use list.sort() method.

>>> lis = [[1,4,7],[3,6,9],[2,59,8]]
>>> lis.sort()
>>> lis
[[1, 4, 7], [2, 59, 8], [3, 6, 9]]

If you want to do a reverse sort, you can use lis.reverse() after lis.sort()

>>> lis.reverse()
>>> lis
[[3, 6, 9], [2, 59, 8], [1, 4, 7]]

Answer 3

li = [[1,4,7],[3,6,9],[2,59,8]]
li.sort(key=lambda x: int(x[0]))

This will sort in place changing the original list though. If you want to keep the original list, it is better to use:

sorted(li, key = lambda x: int(x[0]))