[GRASS-user] Copy and concatenate a vector attribute between layers

[Markus Metz]

On Thu, Dec 7, 2017 at 9:21 AM, Moritz Lennert <mlennert at club.worldonline.be>
wrote:
>
>
>
> Am 6. Dezember 2017 19:45:49 MEZ schrieb Peter Tittmann <
ptittmann at gmail.com>:
> >Moritz,
> >
> >v.db.connect -p c34_patch
> >Vector map <c34_patch> is connected by:
> >layer <1/c34_patch> table <c34_patch> in database
> ></Users/pete/grassdata/<FOO>/project_area/sqlite/sqlite.db> through
> >driver <sqlite> with key <cat>
> >
> >So it seems that only layer 1 is connected.
> >
> >When try to connect layer 2:
> >
> >v.db.connect map=c34_patch at project_area table=c34_patch layer=2
> >ERROR: Use -o to overwrite existing link for layer <2>
>
> This is weird. This message normally only comes when there really is a
connection defined for this layer:

The reason for the error could be that the table c34_patch is already
attached to layer 1.

I guess what is needed here is v.db.addtable map=c34_patch layer=2

Now you could proceed as suggested by Moritz:

- Create a new column in layer 1 where you can put the info from layer 2
- Fill this column with v.to.db option=query query_layer=2, etc
- Create a second new column to hold the concatenation
- v.db.update to update this new column with the concatenation of the two
others (something like qcol = "STRATA || '_' || STAND")

Markus M

>
> GRASS 7.2.2 (nc_spm_08):~ > g.copy v=hospitals,test
> Copy vector <hospitals at PERMANENT> to current mapset as
> <test>
>  GRASS 7.2.2 (nc_spm_08):~ > v.db.connect -p test
> Vector map <test> is connected by:
> layer <1/hospitals> table <test> in database
</data/home/mlennert/GRASSDATA/nc_spm_08/user1/sqlite/sqlite.db>
> through driver <sqlite> with key <cat>
> GRASS 7.2.2 (nc_spm_08):~ > v.db.connect test layer=2 table=test
> The table <test> is now part of vector map <test> and may be deleted or
> overwritten by GRASS modules
> Select privileges were granted on the table
> GRASS 7.2.2 (nc_spm_08):~ > v.db.connect -p test
> Vector map <test> is connected by:
> layer <1/hospitals> table <test> in database </data/hom
> e/mlennert/GRASSDATA/nc_spm_08/user1/sqlite/sqlite.db>
> through driver <sqlite> with key <cat>
> layer <2/test> table <test> in database
</data/home/mlennert/GRASSDATA/nc_spm_08/user1/sqlite/sqlite.db> through
driver <sqlite> with key <cat>
> GRASS 7.2.2 (nc_spm_08):~ > v.db.connect test layer=2 table=test
> ERROR: Use -o to overwrite existing link for layer <2>
>
> So I don't really understand why you get the error message...
>
> >
> >I’m little unclear on the ‘table’ argument, maybe that should be a now
> >table?
>
> Although there might be situations where one could want to connect two
layers to the same table, generally each layer is connected to a different
table.
>
> In your original post you said the vector had two layers with attributes.
This does not seem to be the case when I see the v.db.connect -p output.
Maybe if you go a bit back and explain to us in what format the original
data is and how you imported it, this might help us help you.
>
> Moritz
>
> >
> >Thanks very much.
> >
> >Peter
> >> On Dec 6, 2017, at 10:27 AM, Moritz Lennert
> ><mlennert at club.worldonline.be> wrote:
> >>
> >>
> >>
> >> Am 6. Dezember 2017 18:42:22 MEZ schrieb Peter Tittmann
> ><ptittmann at gmail.com <mailto:ptittmann at gmail.com>>:
> >>> Thank you, Moritz.
> >>>
> >>> I'm pretty familiar with SQL but can’t figure out how layer 2 is
> >stored
> >>> in the database. When I `pragma table_info(<vector>)` I only see the
> >>> layer 1 attributes.
> >>
> >> v.db.connect -p (or grass.script.vector_db() )will show you all
> >connections between the map and database tables.
> >>
> >>
> >> Moritz
> >>>
> >>> I’ll work with the GRASS approach you suggested.
> >>>
> >>> Best,
> >>> Peter
> >>>
> >>>
> >>>> On Dec 1, 2017, at 11:53 PM, Moritz Lennert
> >>> <mlennert at club.worldonline.be> wrote:
> >>>>
> >>>> On 02/12/17 02:03, Peter Tittmann wrote:
> >>>>> Hi,
> >>>>> I have a vector (`POINT`) which has two layers containing relevant
> >>> attributes (’strata’ and ’stand’). I would like to concatenate the
> >two
> >>> values into a new attribute for Layer 1 (’<STRATA>_<STAND>’). I’ve
> >been
> >>> struggling to sort this out for too long and am tapping out. Its
> >>> probably blatantly obvious but it has escaped me.
> >>>>
> >>>>
> >>>> Probably the easiest way if your not very familiar with SQL:
> >>>>
> >>>> - Create a new column in layer 1 where you can put the info from
> >>> layer 2
> >>>> - Fill this column with v.to.db option=query query_layer=2, etc
> >>>> - Create a second new column to hold the concatenation
> >>>> - v.db.update to update this new column with the concatenation of
> >the
> >>> two others (something like qcol = "STRATA || '_' || STAND")
> >>>>
> >>>> Otherwise, if there is a common key in both tables, you can just
> >>> create a new column and use db.execute to launch a UPDATE TABLE
> >>> directly, grabbing the info from the two table and concatenating it
> >>> directly in the query.
> >>>>
> >>>> Moritz
> >>>>
> >>>>
> >>>>> Thank you!
> >>>>> Here are some specifics.
> >>>>> east, north: 651849.842735, 6604949.78485
> >>>>> c34_patch at project_area:
> >>>>>  Type: Point
> >>>>>  Id: 21622
> >>>>>  Layer: 1
> >>>>>  Category: 21623
> >>>>>  Driver: sqlite
> >>>>>  Database:
> >>> /Users/pete/grassdata/PortGraham/project_area/sqlite/sqlite.db
> >>>>>  Table: c34_patch
> >>>>>  Key_column: cat
> >>>>>  Attributes:
> >>>>>    cat: 21623
> >>>>> *strata: 3  — STRATA*
> >>>>> c34_patch at project_area:
> >>>>>  Type: Point
> >>>>>  Id: 21622
> >>>>>  Layer: 2
> >>>>> *Category: 10  — STAND*
> >>>>> _______________________________________________
> >>>>> grass-user mailing list
> >>>>> grass-user at lists.osgeo.org <mailto:grass-user at lists.osgeo.org>
> ><mailto:grass-user at lists.osgeo.org <mailto:grass-user at lists.osgeo.org>>
> >>>>> https://lists.osgeo.org/mailman/listinfo/grass-user
> ><https://lists.osgeo.org/mailman/listinfo/grass-user>
> >>> <https://lists.osgeo.org/mailman/listinfo/grass-user
> ><https://lists.osgeo.org/mailman/listinfo/grass-user>>
> _______________________________________________
> grass-user mailing list
> grass-user at lists.osgeo.org
> https://lists.osgeo.org/mailman/listinfo/grass-user
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/grass-user/attachments/20171207/87485e55/attachment-0001.html>