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

[César Augusto Ramírez Franco]

On Thu, Feb 14, 2019, 19:25 Daniel Victoria <daniel.victoria at gmail.com
wrote:

> Never tried it but you got me curious.
>
> It looks simpler to define a new function or the database using python
> sqlite3 libs
>
>
> https://docs.python.org/2/library/sqlite3.html#sqlite3.Connection.create_function
>
> Cheers
>

Thanks for the suggestion, this seems still kind of complex to do without
proper programming knowledge, I'll try Markus' suggestion on monday, it
seems like a much nicer approach than trying to explain numpy in the python
console to students.

On Thu, Feb 14, 2019 at 12:50 PM César Augusto Ramírez Franco <
> caesarivs at gmail.com> wrote:
>
>> 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, 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*
>> _______________________________________________
>> grass-user mailing list
>> grass-user at lists.osgeo.org
>> https://lists.osgeo.org/mailman/listinfo/grass-user
>
>
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