<div dir="ltr"><br><div class="gmail_extra"><br><div class="gmail_quote">On Wed, Sep 30, 2015 at 11:20 AM, Paulo van Breugel <span dir="ltr"><<a href="mailto:p.vanbreugel@gmail.com" target="_blank">p.vanbreugel@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex">
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<div>On 30-09-15 16:18, Anna Petrášová
wrote:<br>
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<div class="gmail_quote">On Wed, Sep 30, 2015 at 9:27 AM,
Paulo van Breugel <span dir="ltr"><<a href="mailto:p.vanbreugel@gmail.com" target="_blank"></a><a href="mailto:p.vanbreugel@gmail.com" target="_blank">p.vanbreugel@gmail.com</a>></span>
wrote:<br>
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<div class="gmail_quote"><span>On Wed, Sep
30, 2015 at 11:53 AM, Pietro <span dir="ltr"><<a href="mailto:peter.zamb@gmail.com" target="_blank"></a><a href="mailto:peter.zamb@gmail.com" target="_blank">peter.zamb@gmail.com</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex">On
Wed, Sep 30, 2015 at 9:51 AM, Paulo van Breugel<br>
<span><<a href="mailto:p.vanbreugel@gmail.com" target="_blank">p.vanbreugel@gmail.com</a>>
wrote:<br>
><br>
><br>
> On Wed, Sep 30, 2015 at 2:02 AM, Anna
Petrášová <<a href="mailto:kratochanna@gmail.com" target="_blank">kratochanna@gmail.com</a>><br>
> wrote:<br>
>><br>
>><br>
>><br>
>> On Tue, Sep 29, 2015 at 6:09 PM,
Paulo van Breugel<br>
>> <<a href="mailto:p.vanbreugel@gmail.com" target="_blank">p.vanbreugel@gmail.com</a>>
wrote:<br>
>>><br>
>>> This must be a very basic
question, but I can't find an easy/direct way<br>
>>> to do this. In python, if I have
an array with values with a length equal to<br>
>>> the number of rows in an
attribute table of a (point) vector layer, how
can<br>
>>> I write those values to a new
column in that attribute table. I can of<br>
>>> course first create the column,
but than how to update that column with the<br>
>>> values in the array?<br>
>><br>
>><br>
>> it should be pretty easy to do with
pygrass, unfortunately there is no<br>
>> example on assigning attributes in
the official documentation [1], but it<br>
>> should be pretty easy, something like
that (not tested):<br>
>><br>
>> with VectorTopo('myvector', mode='w')
as vectormap:<br>
>> for feature in vectormap:<br>
>> feature.attrs['mycolumn'] =
value<br>
>><br>
>><br>
> Thanks, but that seems to write the
vector back without attribute table<br>
<br>
</span>You have to save the changes in the
database out from your cycle, with:<br>
<br>
vectormap.table.conn.commit()<br>
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<div>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.,<br>
<br>
<span style="font-family:monospace,monospace">#
Create vector<br>
grass.run_command("v.random", output="testB",
npoints=10, overwrite=True)<br>
grass.run_command("v.db.addtable", map="testB",
columns="X DOUBLE PRECISION,Y DOUBLE
PRECISION,GR INTEGER")<br>
grass.run_command("v.to.db", map="test",
option="coor", columns="X,Y")<br>
<br>
# Create groups<br>
vectmap = 'test'<br>
cvals = array(grass.vector_db_select(vectmap,
layer = int(1), columns =
'X,Y')['values'].values()).astype(np.float)<br>
centroids,_ = kmeans(cvals,2)<br>
idx,_ = vq(cvals,centroids)<br>
<br>
</span></div>
<div><span style="font-family:monospace,monospace">#
write results to tabel<br>
</span></div>
<div><span style="font-family:monospace,monospace">Now
I would like to write idx to the column 'GR' in
the attribute table of 'test'.<br>
</span><br>
</div>
<div>p.s. I am first creating the XY columns now,
but is there a function to get the coordinates
(cvals) in pygrass directly?<br>
</div>
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<div>I don't fully understand the example, </div>
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Thanks for the quick response. I basically have a list with values
(idx in the example above) which I like to add as a column to the
attribute table of an existing vector (point layer). The length of
idx is equal to the number of rows in the attribute table. The
solution of Anna seems like an elegant solution (and easier and more
flexible than other solutions I tried using e.g., sqlite3). However,
as I wrote, I end up with a vector without attribute table. You
wrote that I "have to save the changes in the database out from your
cycle, with: vectormap.table.conn.commit()". I am, however, not sure
what you mean with 'out from your cycle' or how to implement that. <br></div></blockquote><div><br></div><div>probably after the for cycle ends you would call this 'vectormap.table.conn.commit()', if it doesn't works, try to put it in the cycle (I am not sure what is supposed to work).</div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div text="#000000" bgcolor="#FFFFFF"><span class="">
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<div>but yes, you can get coordinates:</div>
<div><br>
</div>
<div><font face="monospace, monospace"><span style="font-size:12.8px">with VectorTopo('myvector',
mode='w') as vectormap:</span><br style="font-size:12.8px">
<span style="font-size:12.8px"> for feature
in vectormap:</span><br style="font-size:12.8px">
<span style="font-size:12.8px"> print feature.x</span></font><br>
</div>
<div><span style="font-family:monospace,monospace;font-size:12.8px">
print feature.y</span><font face="monospace,
monospace"><span style="font-size:12.8px"><br>
</span></font></div>
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<br></span>
Great, thanks. I did not find this in the manual. If it is not
there, perhaps it would be something worth including? I would not
mind providing a text, but I am not sure what would be the best way
to do that.<br></div></blockquote><div><br></div><div>Technically, it's in the manual:</div><div><a href="https://grass.osgeo.org/grass70/manuals/libpython/pygrass_vector.html#geometry-classes">https://grass.osgeo.org/grass70/manuals/libpython/pygrass_vector.html#geometry-classes</a></div><div><br></div><div>but we are lacking more examples of often used constructions. Some other examples are available in the recent workshop we did:</div><div><br></div><div><a href="https://github.com/wenzeslaus/python-grass-addon/blob/master/02_pygrass_library.ipynb">https://github.com/wenzeslaus/python-grass-addon/blob/master/02_pygrass_library.ipynb</a><br></div><div><br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div text="#000000" bgcolor="#FFFFFF">
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<div> <br>
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Pietro<br>
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