How do I sort a nested list by the second value and then the first, without using packages?

Question

I have a nested list of pairs of numbers:

>>> l = [[0, 0], [1, 3], [3, 2], [3, 4], [4, 6], [5, 2], [3, 1], [1, 6], [5, 4], [4, 3], [2, 5], [3, 0]]

Is it possible to sort the list by the second term and then the first without using packages? The desired output is this:

>>> sort_two_then_one(l)
[[0, 0], [3, 0], [3, 1], [3, 2], [5, 2], [1, 3], [4, 3], [3, 4], [5, 4], [2, 5], [1, 6], [4, 6]]

What do yo mean by packages? – Dani Mesejo Apr 05 '20 at 21:14 — Dani Mesejo, Apr 05 '20 at 21:14
@DaniMesejo: like not using `operator` module. – mechanical_meat Apr 05 '20 at 21:15 — mechanical_meat, Apr 05 '20 at 21:15
@Hiwafreak: have you tried anything? – mechanical_meat Apr 05 '20 at 21:16 — mechanical_meat, Apr 05 '20 at 21:16

score 1 · Accepted Answer · answered Apr 05 '20 at 21:17

1

Here is the answer:

Code

lst = [[0, 0], [1, 3], [3, 2], [3, 4], [4, 6], [5, 2], [3, 1], [1, 6], [5, 4], [4, 3], [2, 5], [3, 0]]

sorted_list = sorted(sorted(lst, key=lambda x: x[0]), key=lambda x: x[1])

print(sorted_list)

Output

[[0, 0],
 [3, 0],
 [3, 1],
 [3, 2],
 [5, 2],
 [1, 3],
 [4, 3],
 [3, 4],
 [5, 4],
 [2, 5],
 [1, 6],
 [4, 6]]

answered Apr 05 '20 at 21:17

Rahul P

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While this works, the list needs to be sorted twice. It is possible to sort by multiple indices in one call to `sorted`. – Lydia van Dyke Apr 05 '20 at 21:22

score 0 · Answer 2 · answered Apr 05 '20 at 21:18

0

Seems to be a duplicate of Python sorting by multiple criteria

sorted(l, key=lambda x: (x[1], x[0]))
>>> [[0, 0], [3, 0], [3, 1], [3, 2], [5, 2], [1, 3], [4, 3], [3, 4], [5, 4], [2, 5], [1, 6], [4, 6]]

answered Apr 05 '20 at 21:18

Lydia van Dyke

2,466
3
13
25

score 0 · Answer 3 · answered Apr 05 '20 at 21:18

0

You can use the optional key argument of sorted() and implement a lambda function. These are all built-in methods of python. See also this

a=[[0, 0], [1, 3], [3, 2], [3, 4], [4, 6], [5, 2], [3, 1], [1, 6], [5, 4], [4, 3], [2, 5], [3, 0]]

print(sorted(a, key = lambda x: x[1]))

output

[[0, 0], [3, 0], [3, 1], [3, 2], [5, 2], [1, 3], [4, 3], [3, 4], [5, 4], [2, 5], [4, 6], [1, 6]]

[Program finished]

answered Apr 05 '20 at 21:18

Björn

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This does not sort by the first term. Result does not equal the desired output. – Lydia van Dyke Apr 05 '20 at 21:21
@LydiavanDyke it does exactly match the desired output? – Björn Apr 05 '20 at 21:23
1

Last item should be [4,6]. Yours is [1,6]. You have to scroll to the very end. The question clearly states "by the second term and then the first". The example could have been chosen a bit more user friendly though :) – Lydia van Dyke Apr 05 '20 at 21:26
You are right!! – Björn Apr 05 '20 at 21:33

How do I sort a nested list by the second value and then the first, without using packages?

3 Answers3