On Wed, Sep 30, 2015 at 11:53 AM, Pietro <[email protected]> wrote:
> On Wed, Sep 30, 2015 at 9:51 AM, Paulo van Breugel > <[email protected]> wrote: > > > > > > On Wed, Sep 30, 2015 at 2:02 AM, Anna Petrášová <[email protected]> > > wrote: > >> > >> > >> > >> On Tue, Sep 29, 2015 at 6:09 PM, Paulo van Breugel > >> <[email protected]> wrote: > >>> > >>> This must be a very basic question, but I can't find an easy/direct way > >>> to do this. In python, if I have an array with values with a length > equal to > >>> the number of rows in an attribute table of a (point) vector layer, > how can > >>> I write those values to a new column in that attribute table. I can of > >>> course first create the column, but than how to update that column > with the > >>> values in the array? > >> > >> > >> it should be pretty easy to do with pygrass, unfortunately there is no > >> example on assigning attributes in the official documentation [1], but > it > >> should be pretty easy, something like that (not tested): > >> > >> with VectorTopo('myvector', mode='w') as vectormap: > >> for feature in vectormap: > >> feature.attrs['mycolumn'] = value > >> > >> > > Thanks, but that seems to write the vector back without attribute table > > You have to save the changes in the database out from your cycle, with: > > vectormap.table.conn.commit() > Thanks Pietro. I am, however, not sure I understand (I tried to use it, but thanks to my limited experience in Python / pygrass not much luck). Just to be more specific, I am trying to create a script that divides points in training and test groups, similar to v.kcv, but with points clustered in space. E.g., # Create vector grass.run_command("v.random", output="testB", npoints=10, overwrite=True) grass.run_command("v.db.addtable", map="testB", columns="X DOUBLE PRECISION,Y DOUBLE PRECISION,GR INTEGER") grass.run_command("v.to.db", map="test", option="coor", columns="X,Y") # Create groups vectmap = 'test' cvals = array(grass.vector_db_select(vectmap, layer = int(1), columns = 'X,Y')['values'].values()).astype(np.float) centroids,_ = kmeans(cvals,2) idx,_ = vq(cvals,centroids) # write results to tabel Now I would like to write idx to the column 'GR' in the attribute table of 'test'. p.s. I am first creating the XY columns now, but is there a function to get the coordinates (cvals) in pygrass directly? > > Pietro >
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