Python Sorting Lists based on Values inside the List (from right to left)

Question

With Python, how to sort the lists based on the values in the list (from right to left)?

For example:

[2005, 6, 21], [2003, 5, 21], [2005, 5, 11], [2003, 5, 22]

should return

[2003, 5, 21], [2003, 5, 22], [2005, 5, 11], [2005, 6, 21]

`sorted([[2005, 6, 21], [2003, 5, 21], [2005, 5, 11], [2003, 5, 22]])` ? — Epsi95, Jun 29 '21 at 04:49
`sorted(a)` or `a.sort()` both will do, as the default sorting order is left to right — Osman Mamun, Jun 29 '21 at 04:49
`l = [[2005, 6, 21], [2003, 5, 21], [2005, 5, 11], [2003, 5, 22]]` `l.sort()` — Lei Yang, Jun 29 '21 at 04:49
Did no-one else notice the "right to left" bit in the question? It seems to be inconsitent with the expected result. — paxdiablo, Jun 29 '21 at 05:04
Does this answer your question? [sorting a list in python](https://stackoverflow.com/questions/17608210/sorting-a-list-in-python) — Jonath Sujan, Jun 29 '21 at 05:22

paxdiablo · Answer 1 · 2021-06-29T05:19:04.060

Based on your expected result, that's not right-to-left sorting. In that case, the default sort works just fine:

>>> xyzzy = [[2005, 6, 21], [2003, 5, 21], [2005, 5, 11], [2003, 5, 22]]
>>> sorted(xyzzy)
[[2003, 5, 21], [2003, 5, 22], [2005, 5, 11], [2005, 6, 21]]

If you did want to sort based on right-to-left order in each sub-list, you can provide a key function/callable which does the work for you. Since you want the same comparison but in reverse, just use the reversed list for the comparison:

>>> sorted(xyzzy, key=lambda x: x[::-1])
[[2005, 5, 11], [2003, 5, 21], [2005, 6, 21], [2003, 5, 22]]

Jonath Sujan · Answer 2 · 2021-06-29T05:20:21.330

Use the sorted() in python.

input_list = [2005, 6, 21], [2003, 5, 21], [2005, 5, 11], [2003, 5, 22]
sorted_list = sorted(input_list)

Declaring the input_list like above will create a tuple of lists and input_list.sort() will not work as sort does not support tuple. If you need to use sort(), you have to first convert the tuple of lists to list of lists and then perform sort operation like below.

input_list = [[2005, 6, 21], [2003, 5, 21], [2005, 5, 11], [2003, 5, 22]]
input_list.sort()

If you need to sort from left to right, you can use the reverse parameter.

sorted_list = sorted(input_list, reverse=True)

or

input_list.sort(reverse=True)

Note that sorted() will return the sorted list, whereas sort() will replace the input list with the sorted list.

Python Sorting Lists based on Values inside the List (from right to left)

2 Answers2