[GRASS-user] Uploading NumPy array as a new column to a vector map

[Markus Neteler]

Hi,

Am Do., 14. Feb. 2019, 15:50 hat César Augusto Ramírez Franco <
caesarivs at gmail.com> geschrieben:

> Greetings,
>
> I have a municipality polygon layer with a poverty index (percent) and a
> population count, I'm multiplying them to visualize the vulnerability for
> each municipality, due to the distribution of that new variable I want to
> compute the logarithm, which is not possible in sqlite,
>

Yes but there is an extension for this.

See
https://grasswiki.osgeo.org/wiki/Build_SQLite_extension_on_Linux

It may solve the issue.

Best
Markus



so I tried reading the column with numpy and issuing a np.log10(). I'm
> happy with the result, but how can I get this new numpy array to a new
> column in the vector map in a simple way?
>
> This is what I already have:
>
> #!/usr/bin/env python
>
> import grass.script as gs
> import numpy as np
> import matplotlib.pyplot as plt
>
> nbi_pob = np.array(gs.vector_db_select("muniant", columns =
> "nbi_pob")["values"].values()).astype(float).squeeze()
>
> plt.hist(nbi_pob)
> plt.show()
>
> log_nbi_pob = np.log10(nbi_pob)
>
> plt.hist(log_nbi_pob)
> plt.show()
>
> I'm trying to introduce this kind of analysis to students who are not
> familiar nor proficient with programming (this is an GIS introductory
> course) so the numpy bit is already complex enough to them, and I'd like to
> avoid using for loops with cursors to achieve this.
>
> Is there a simple solution to this?
>
> --
> *César Augusto Ramírez Franco*
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