[GRASSLIST:3671] Re: v.extract (5.7) doesn't work on extra fields?

[William K]

>>> 3) > v.extract -d in=tgr out=tgrzip type=area,centroid field=4
>>> list=1-99999
>>>    This is wrong as it groups areas by category, not by ZIP.
>>
>> so v.extract -d works purely on categories?  I guess I was thinking
>> that cats were like a table relate to the fields, and it would use the
>> field columns (minus the cat).
>
> 'list' and 'file' works on categories, 'where' works on attributes.
>
so if I used: (assuming the tables are sorted correctly so that _2.cat 
= _3.cat)

field=3 where "ZCTA != ''"

would it also dissolve by ZCTA?  or just select?  I tried where once 
with no luck, but I was selecting on the cat column (where "cat > 0"), 
so of course there was no difference.  Or maybe not because ZCTA5 is 
varchar?  oh, that's probably why you did the whole reclass thing in 
the first place - dissolve only works on the cat.

oh, but that would be nice for dissolve...

>>> 4) There was a bug in v.extract -d, I fixed that in cvs.
>>
>> I'm using CVS snapshots (2004-6-5 at that time).  I had heard about 
>> the
>> bug fix and wanted to try it out.
>
> It was fixed today.
>
huh, I thought I saw it mentioned a couple weeks ago.  maybe you were 
just talking about fixing it and I jumped the gun.

well, I have stuff to keep me busy, so I'll just wait for the next 
snapshot.

-----
William Kyngesburye <williamk at mappingspecialists.com>
Mapping Specialists <http://www.mappingspecialists.com>

Don't Panic