[GRASS-user] Reclassify a vector adding a column

[Stefan Blumentrath]

Ciao Madi,

You could use db.execute and do something like:
db.execute sql="ALTER TABLE vectormap ADD COLUMN reclass_column TEXT;
UPDATE vectormap SET reclass_column = CASE
     WHEN old_column = ' old value 1' THEN ' new value 1'
     WHEN old_column = ' old value 2' THEN ' new value 2'
     WHEN old_column = ' old value 3' THEN ' new value 3'
     ELSE ' new value 4'
END; "

Maybe worth adding as an (validated) example to the manual of db.execute (https://grass.osgeo.org/grass78/manuals/db.execute.html)…

Cheers
Stefan

P.S.: I did not alidate the SQL syntax, but it should be roughly along those lines…

From: grass-user <grass-user-bounces at lists.osgeo.org> On Behalf Of Margherita Di Leo
Sent: onsdag 17. juni 2020 10:35
To: GRASS user list <grass-user at lists.osgeo.org>
Subject: [GRASS-user] Reclassify a vector adding a column

Hi,

I need to reclassify a vector in the following way: based on a column of type string I have to create a new column of type string based on certain rules that I give upon the first column, and I thought it would be really handy if I could do it like  CASE WHEN... THEN ...
I have tried to feed a similar rules file to v.reclass but this statement is not recognised. How can I translate it? Furthermore, I would like to be able to just add a reclass column rather than creating a new vector file, is that possible? How?

Thank you in advance

Kind regards,

--
Margherita Di Leo
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