[GRASS-user] update cat column in vector data set

[Moritz Lennert]

On Fri, August 17, 2012 13:21, Stefan Luedtke wrote:
> Thanks, that did the trick.
>
> I guess, in order to get a consecutive "cat", I do have to reclass
> (v.reclass) the vector- or is there any shortcut?

v.category option=del
v.category option=add

but this will erase any connections to attributes that you might have.

If you have attributes, v.reclass is probably your best bet. But why do
your cats have to be consecutive ?

Moritz


>
> Sorry for the noise, but vector stuff  in grass is still a bit confusing
> to me.
>
> Cheers,
>
> Stefan
>
> On Fri, 2012-08-17 at 11:38 +0200, Moritz Lennert wrote:
>
>> On 16/08/12 20:23, Stefan Luedtke wrote:
>> > That helped for my general understanding, thanks a lot, but I can not
>> > figure out how.
>> >
>> > Can anyone just give a few hints on the procedure, basically, how to
>> > continue after "v.clean", please?
>>
>> You could try using v.extract with something list list=1-9999 in order
>> to create a new vector file which contains only those polygons (and
>> their attributes in the table) which exist in your cleaned file.
>>
>> Moritz
>>
>> >
>> > Cheers,
>> >
>> > Stefan
>> >
>> > On Thu, 2012-08-16 at 16:29 +0200, Markus Metz wrote:
>> >> On Thu, Aug 16, 2012 at 1:10 PM, Stefan
>> Luedtke<sluedtke at gfz-potsdam.de  <mailto:sluedtke at gfz-potsdam.de>>
>> wrote:
>> >> >  Dear friends,
>> >> >
>> >> >  I am struggling with the following point.
>> >> >
>> >> >  I have created a shape of subbasins based on a raster data set.
>> Since this
>> >> >  yields some tiny (pixel size) areas, I run"v.clean"  with a
>> certain
>> >> >  threshold to remove/append those artifacts. However, the resulting
>> vector
>> >> >  data set still holds all categories of the old one, even so, some
>> areas have
>> >> >  been removed.
>> >>
>> >> This is because several areas can belong to the same category, e.g.
>> >> basin id, and the category of a deleted area may still be used by
>> >> another, existing area. BTW, it is not uncommon that one raster basin
>> >> is represented by several vector areas.
>> >> >
>> >> >  So my question: How can I update these values that the number of
>> categories
>> >> >  matches the number of areas?
>> >>
>> >> You can delete the table and create a new table. Otherwise, entries
>> in
>> >> the attribute table that are no longer used do not do harm.
>> >>
>> >> HTH,
>> >>
>> >> Markus M
>> >>
>> >> >
>> >> >  I tried v.category (but der is not update function).
>> >> >
>> >> >  Cheers,
>> >> >
>> >> >  Stefan
>> >> >
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>> >> >
>> >
>> >
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>