How to sort a list of x-y coordinates

Question

I need to sort a list of [x,y] coordinates that looks like this:

list = [[1,2],[0,2],[2,1],[1,1],[2,2],[2,0],[0,1],[1,0],[0,0]]

The pattern I'm looking for after sorting is:

[x,y] coordinate shall be sorted by y first and then by x. The new list should look like:

list = [[0,0],[1,0],[2,0],[0,1],[1,1],[2,1],[0,2],[1,2],[2,2]]

I can't figure out how to do it and would appreciate some help.

Also the faster and cleaner answer isn't here. Which would be `my_list = np.array(list) ind = np.lexsort((my_list[:,1], mylist[:,0])) sorted = my_list[ind]` — Jesse Reza Khorasanee, May 14 '19 at 23:13

AKS · Accepted Answer · 2016-05-09T09:31:15.713

54

use sorted with key:

>>> my_list = [[1,2],[0,2],[2,1],[1,1],[2,2],[2,0],[0,1],[1,0],[0,0]]
>>> sorted(my_list , key=lambda k: [k[1], k[0]])
[[0, 0], [1, 0], [2, 0], [0, 1], [1, 1], [2, 1], [0, 2], [1, 2], [2, 2]]

It will first sort on the y value and if that's equal then it will sort on the x value.

I would also advise to not use list as a variable because it is a built-in data structure.

edited May 09 '16 at 09:31

answered May 09 '16 at 09:13

AKS

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No problem. Nice answer! – Rory Daulton May 09 '16 at 09:33
Cool, but if I want to 1) sort by y 2@ sort by x, how to do it in this? – Liping Huang Sep 06 '19 at 00:59
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my_updated_list = sorted(my_list , key=lambda k: [k[1], k[0]]), you have to assign that to new variable. – Antti Jun 24 '20 at 16:25
@LipingHuang That is exactly what this method does. See Antti's comment. If you wanted it the other way around, swap k[1] with k[0]. – ReinstateMonica3167040 Oct 31 '20 at 15:10
in python 3.10 you need to re assign the return value from sorted back to the list: `my_list = sorted(...)` – ThunderWiring Dec 14 '22 at 11:41

score -3 · Answer 2 · answered May 09 '16 at 09:26

-3

Define a virtual index Z = (X+Y) now perform quick sort on Z and based on index Z pick elements (X, Y). Points on circle will lead to same Z (and obviously will stick together in sort results)

answered May 09 '16 at 09:26

SACn

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this can't work because the coordinates `(3,11)` and `(11,3)` would give you the same `Z` when in reality they're very different points – Jona May 10 '19 at 20:47

How to sort a list of x-y coordinates

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