[R] use R from python

[Barry Rowlingson]

On Thu, Jan 21, 2010 at 8:35 PM, Massimo Di Stefano
<massimodisasha at yahoo.it> wrote:
> Hi All,
>
> please aplogize me if my qustion is a bit OT here,
> but maybe is there someone that uses R from inside python
> using rpy or rpy2 interface.

> In [54]: x = rdiv( ( rdiff( x, rmin(x) ) ) , ( rdiff( rmax(x) , rmin(x) ) ) )
>
> In [55]: y = rdiv( ( rdiff( r_sorted, rmin(r_sorted) ) ) , ( rdiff( rmax(r_sorted) , rmin(r_sorted) ) ) )
> Errore in .Primitive("-")("mymap at data$elevation.dem", "mymap at data$elevation.dem") :
>  argomento non numerico trasformato in operatore binario
> ------------------------------------------------------------
> Traceback (most recent call last):
>  File "<ipython console>", line 1, in <module>
>  File "build/bdist.macosx-10.6-universal/egg/rpy2/robjects/__init__.py", line 423, in __call__
> RRuntimeError: Errore in .Primitive("-")("mymap at data$elevation.dem", "mymap at data$elevation.dem") :
>  argomento non numerico trasformato in operatore binario

 My non-existent Italian is telling me this is non-numeric argument in
binary operator. Something like:

> "hello" - "goodbye"
Error in "hello" - "goodbye" : non-numeric argument to binary operator

 - because you are subtracting the strings "mymap at data$elevation.dem".

 Tracking back, those strings come from:

r_sorted = rsort('mymap at data$elevation.dem', decreasing=True)

 - which is sorting the string vector! Like this:

> sort('mymap at data$elevation.dem', decreasing=TRUE)
[1] "mymap at data$elevation.dem"

 You want to sort the *value* of that object.  You want to sort the
$elevation.dem column of the @data slot of the python R object mymap.

 In a functional form which will translate to your style of rpy2 would
be this in R:

get("$")(slot(mymap,"data"),"elevation.dem")

 You may need to get 'get' and 'slot' from r.robjects in the way you
do other functions. This looks a bit weird to me, but I'm used to
rpy-1 - maybe rpy 2 is like this!

 Hope that points you in the right direction.

Barry

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