[GRASS-user] Resetting vector cats and/or a quick exchange between numpy and vector tables

[Michel Wortmann]

Thanks for your help Markus, see below.

On 02/23/2014 11:32 PM, Markus Neteler wrote:
> On Fri, Feb 21, 2014 at 3:06 PM, Michel Wortmann
> <wortmann at pik-potsdam.de> wrote:
>> Hi list,
>> I have some (basic) vector related questions:
>>
>> After cleaning a vector map, it doesnt have continuous (i.e. no gaps in
>> numbering) categories, how do I efficiently reset these to so that they have
>> regular increments (i.e. 1) again? r.clump does something very similar with
>> vectors. I have tried dropping and adding a new table, deleting and adding
>> categories with v.category. I thought v.reclass may do the trick but I'd
>> first need a column with continuous numbers for that.
> Hi Michel,
>
> perhaps using v.category on layer=2 would to the trick to add new categories?
This doesnt seem to do the trick for me. I've resorted to the somewhat 
ungraceful quickfix of converting it to raster and back to vector again 
until I come across a better solution.
>> Somewhat related to this, what is the best/most efficient way of updating an
>> entire column of a vector table from a numpy array. v.update does do it for
>> one entry only, i.e. looping would be possible, but that takes ages. Would I
>> have to go back to using basic sqlite3 packages for that?
> If you only want to work on a table, then db.execute:
> http://grass.osgeo.org/grass70/manuals/db.execute.html
>
> might be the best. To speed up, put the statements into an SQL transaction.
Yes this is indeed quicker, although this is probably not the most 
convenient method.
>
> best,
> Markus
>