如何对 python 中的二维列表进行排序？

Question

I have a list of co-ordinates which indicate the top-left position (first two values) and the bottom right co-ordinates (the last two) of a detected word in an image

It looks something like this:

boxes= [[ 27,  22,  84 , 54],
     [261 ,127 ,294 ,163],
     [224 , 21 ,279 , 54],
     [ 45  ,83 , 96 ,111],
     [ 10 ,126 , 66 ,163],
     [189 ,185 ,219 ,222],
     [154 , 21 ,192 , 59],
     [278 , 25 ,318 , 58],
     [146 ,188 ,186, 220]]

so in boxes[0] would give me [27,22,84,54] and lets call them startX, startY, endX, endY respectively

For visualizing:

 (27,22)------------.
    '               '
    '               '
    '               '
    '---------------(84,54)

I need to sort this in a way that startY begins being minimum with increasing startX and startY incresaing

so the output must look something like this

     [[154 , 21 ,192 , 59],
     [224 , 21 ,279 , 54],
     [ 27,  22,  84 , 54],
     [278 , 25 ,318 , 58],
     [ 45  ,83 , 96 ,111],
     [ 10 ,126 , 66 ,163],
     [261 ,127 ,294 ,163],
     [189 ,185 ,219 ,222],
     [146 ,188 ,186, 220]]

Answer 1

Python will sort a tuple based on position, so you can pass a key to sorted() that puts the elements in the order you want to base the sort on:

boxes= [[ 27,  22,  84 , 54],
     [261 ,127 ,294 ,163],
     [224 , 21 ,279 , 54],
     [ 45  ,83 , 96 ,111],
     [ 10 ,126 , 66 ,163],
     [189 ,185 ,219 ,222],
     [154 , 21 ,192 , 59],
     [278 , 25 ,318 , 58],
     [146 ,188 ,186, 220]]

sorted(boxes, key=lambda x: (x[1], x[0], x[2], x[3]))

Result:

[[154, 21, 192, 59],
 [224, 21, 279, 54],
 [27, 22, 84, 54],
 [278, 25, 318, 58],
 [45, 83, 96, 111],
 [10, 126, 66, 163],
 [261, 127, 294, 163],
 [189, 185, 219, 222],
 [146, 188, 186, 220]]

If you want to sort the list in-place use boxes.sort() with the same key.

Answer 2

OK, so what you want is to first sort for startX and then for startY, while respecting the relative order between elements in startX. It would look like this:

# Input:
[[ 27,  22,  84 , 54],
 [261 ,127 ,294 ,163],
 [224 , 21 ,279 , 54],
 [ 45  ,83 , 96 ,111],
 [ 10 ,126 , 66 ,163],
 [189 ,185 ,219 ,222],
 [154 , 21 ,192 , 59],
 [278 , 25 ,318 , 58],
 [146 ,188 ,186, 220]]
# First sort:
[[ 10 ,126 , 66 ,163],
 [ 27,  22,  84 , 54],
 [ 45  ,83 , 96 ,111],
 [146 ,188 ,186, 220],
 [154 , 21 ,192 , 59],
 [189 ,185 ,219 ,222],
 [224 , 21 ,279 , 54],
 [261 ,127 ,294 ,163],
 [278 , 25 ,318 , 58]]
# Second sort:
[[154 , 21 ,192 , 59],
 [224 , 21 ,279 , 54],
 [ 27,  22,  84 , 54],
 [278 , 25 ,318 , 58],
 [ 45  ,83 , 96 ,111],
 [ 10 ,126 , 66 ,163],
 [261 ,127 ,294 ,163],
 [146 ,188 ,186, 220],
 [189 ,185 ,219 ,222]]

That's what's called a stable sort. Now, according to the standard library reference , the sorted function implements a stable sort.