Mapping python tuple and R list with rpy2?

Question

I'm having some trouble to understand the mapping with rpy2 object and python object.

I have a function(x) which return a tuple object in python, and i want to map this tuple object with R object list or vector.

First, i'm trying to do this :

# return a python tuple into this r object tlist
robjects.r.tlist = get_max_ticks(x) 

#Convert list into dataframe
r('x <- as.data.frame(tlist,row.names=c("seed","ticks"))')

FAIL with error : rinterface.RRuntimeError: Error in eval(expr, envir, enclos) : object 'tlist' not found

So i'm trying an other strategy :

robjects.r["tlist"]  = get_max_ticks(x)
r('x <- as.data.frame(tlist,row.names=c("seed","ticks"))')

FAIL with this error : TypeError: 'R' object does not support item assignment

Could you help me to understand ? Thanks a lot !!

Answer 1

Use globalEnv :

import rpy2.robjects as ro
r=ro.r

def get_max_ticks():
    return (1,2)
ro.globalEnv['tlist'] = ro.FloatVector(get_max_ticks())
r('x <- as.data.frame(tlist,row.names=c("seed","ticks"))')
print(r['x'])
#       tlist
# seed      1
# ticks     2

It may be possible to access symbols in the R namespace with this type of notation: robjects.r.tlist , but you can not assign values this way. The way to assign symbol is to use robject.globalEnv .

Moreover, some symbols in R may contain a period, such as data.frame . You can not access such symbols in Python using notation similar to robjects.r.data.frame , since Python interprets the period differently than R . So I'd suggest avoiding this notation entirely, and instead use robjects.r['data.frame'] , since this notation works no matter what the symbol name is.

Answer 2

You could also avoid the assignment in R all together:

import rpy2.robjects as ro
tlist = ro.FloatVector((1,2))
keyWordArgs = {'row.names':ro.StrVector(("seed","ticks"))}
x = ro.r['as.data.frame'](tlist,**keyWordArgs)
ro.r['print'](x)