引用 Z 以外的字母表……即 AA、AB

Question

I have no idea what I am doing with Python. My only experience with it is in QGIS and I am a novice at that too. I have tried to search for something that fits what I am looking for but it's not making sense, maybe because of how it sits within QGIS

I am using QGIS mapping to create Atlas style grids. This has resulted in me finding the following code to apply to a virtual layer…

select *, char(r+64) || ROW_NUMBER() OVER(PARTITION BY r) as newID from (SELECT *,DENSE_RANK() OVER (ORDER BY round( ST_minY(geometry)/0.02) desc) as r FROM Grid ORDER BY round(ST_minY(geometry)/0.02)  DESC, round(ST_minX(geometry)/0.02)  ASC)

From https://gis.stackexchange.com/questions/344161/how-to-create-a-grid-with-customized-labels-in-qgis

My issue is that the char(r+64) bit continues into ASCII symbols and then lowercase after reaching “Z”

Is there a way to modify this code to make it continue beyond Z in the style of excel columns? Ie AA, AB etc.

I don't mind if it is has limits or each reference needs to be typed in.

Answer 1

Here is a quick code to generate a pool of letter identifiers (A->Z, AA->ZZ). There are 702 identifiers, if you need more you can easily add more levels on the same principle.

from string import ascii_uppercase
from itertools import product

pool = list(map(''.join, product(['']+list(ascii_uppercase), list(ascii_uppercase))))

>>> pool
['A', 'B', 'C', ..., 'ZY', 'ZZ']

If you want to map numbers to those, you can use: dict_pool = dict(enumerate(pool))

{0: 'A',
 1: 'B',
 2: 'C',
 3: 'D',
...
 699: 'ZX',
 700: 'ZY',
 701: 'ZZ'}

Answer 2

I came up with this and it works…. I just need to add in extra lines for each time it cycles through 26.

‘select *,
Case
when r<=26 then char(r+64) || ROW_NUMBER() OVER(PARTITION BY r) 
when r between 27 and 52 then 'A' || char(r+38) || ROW_NUMBER() OVER(PARTITION BY r)
else 'B' || char(r+12) || ROW_NUMBER() OVER(PARTITION BY r)

end as newID

from 
(SELECT *,DENSE_RANK() OVER (ORDER BY round( st_minx(geometry)/0.02) asc) as r 
  FROM Grid
  ORDER BY round(ST_minY(geometry)/0.02)  DESC,
           round( ST_minX(geometry)/0.02)  ASC)’