[GRASS-user] Multiple to one question

[Moritz Lennert]

On 16/04/09 06:29, Adam Dershowitz, Ph.D., P.E. wrote:
> I really liked the suggestion, so I tried it....but it doesn't work. 
> To continue my simple example, I did  create view less2 cat,Value
> from data where Value < 2; So I end up with a view, as expected. The
> problem is that if I now link my map to that view, I get an error: No
> attribute found for cat 1 (since the object still tries to link to 
> 1).  And, the same for 2 and 4.  And, I still see the points and
> slashes (ie it still draws point a and puts a null value then a slash
> then 1.1. So is there a way to have it not draw a symbol and not draw
> "null text" when it can't find an attribute?  Since, the whole point
> of what I am trying to do in this case is to eliminate certain data
> with a query?

What do you mean by "eliminate" ?

Maybe you should be more precise about your objectives. Are you trying 
to display something on a map, or not ? If all your looking for is 
tables, than you don't need GRASS at all.


On 16/04/09 07:35, Adam Dershowitz, Ph.D., P.E. wrote:
  > It seems like I should be able to edit the cats, and I tried a few
> different things with v.edit, but I have not had any luck.  I tried
> some things like this: v.edit map=foo tool=catdel -r where="cat > 0" 
> but it gives me: ERROR: Tool catdel requires option cats Although the
> above seems to work with tool=select, which I was using to test
> things about before doing the delete.

As the message says, tool catdel does not work with a select, but you 
have to give it a list of cats. You can do that with something like this:

v.edit map=foo tool=catdel cats=`v.db.select -c foo col=cat where=XYZ | 
awk '{printf"%i,",$1} END{print}'`
(note the back ticks)

> I copied my original vectors, and created the view.  Now what I want
> to do is to delete all the categories in this vector that point to
> null. Is there a way to do that?

Why do you want to do that ? If I understood you correctly, all of these 
cats have a meaning. Maybe not in the currently linked view, but in the 
original table. So if you delete these cats, you will lose the link to 
the values in the original table.

Again, I think we need a better explanation of what it is you are trying 
to get at.

Moritz