On Thu, Jun 25, 2009 at 2:08 PM, reyman<reyma...@gmail.com> wrote:
> Hello guys,
>
> I have a big project for six month, i need a little help about technology
> imbrication ...
>
> 1) Reflexion about System architecture
> > a) I want to make script in python which control/launch R, R access
> data with library "rdbi" and "RdbiPgSQL". I need this to realize simple
> statistics. Do you think it's better to access data in DB with R or with
> python in this case ?
> > b) I want in near futur to create an another type of script wich
> access data in DB with grass by R module "spgrass6" (wich interface R <-->
> GRASS). I need this to make Spatial Analysis
>
> So with my two type of script a) and b) , you think Rpy is a good choice to
> manipulate data/query in R and R <-> GRASS ? Have you an experience in this
> type of plateform/architecture?
I've not used these libraries, but one important question is are you familiar
with both R and python?
> 2) I have problem with RPY and connexion with my DB :
>
> from rpy import *
> import math
>
> r.library("Rdbi")
> r.library("RdbiPgSQL")
>
> r.dbConnect(r.PgSQL(),host="localhost", dbname="simpop", user="postgres",
> password="postgres")
>
> I have this error message :
>
> Traceback (most recent call last):
> ...
> Invalid database class
>
> In R, with the same query, no error ...
That is almost certainly due to the default object conversion, the
most common cause of confusion in rpy beginners.
rPgSQL() returns some database class, which rpy has converted into a
simplified representation using python objects. You then try and pass
this back to the r.dbConnect, which means rpy has to try and turn this
simplified python structure back into R objects. I don't know exactly
what this will look like (maybe an R list), but
it won't be a database object!
You should turn off the conversion.
Try something like this:
import rpy
rpy.set_default_mode(rpy.NO_CONVERSION)
#your code here:
rpy.r.library("Rdbi")
rpy.r.library("RdbiPgSQL")
rpy.r.dbConnect(rpy.r.PgSQL(),host="localhost", dbname="simpop",
user="postgres", password="postgres")
#If you want to go back to the default conversion,
rpy.set_default_mode(rpy.BASIC_CONVERSION)
Peter
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