How to return multiple objects from R script executed in Python

Question

So I am struggling to use the rpy2 package to integrate some workflow between R and Python.

For example, imagine I'm trying to run a Python script that does a linear regression in R and I want to return all of the elements of that (in reality I'm trying to do something much more complicated than this).

I execute the following in Python (calling R; This assumes you have rpy2 installed):

import rpy2.robjects as ro
test = ro.r('''
            # Load in data
            df <- mtcars
            # Run regression
            out = lm(formula='mpg ~ cyl + hp + wt',data=df)
            ''')

And now what? I have a questions:

1. How do I pull the various elements from the result? In R they would be out$coefficients and out$residuals , etc. I know there is documentation for this, but I'm a bit lost. Ideally, I would want the elements in useful formats, so pandas dataframes or indexed lists, etc.

2. What happens to df ? robjects.r() seems to just save whatever the last thing you gave and throw away everything else. I suppose I can work with this, but it's not ideal.

3. Related to 2: Is there a much much better way to do this? In general if someone could put forward a "best practice" for this sort of thing, that would be helpful, since I'm sure that there are many people interested in using Python, but occasionally have a very custom function they need to call using R but they don't want to get to fancy with the integration. Perhaps a way to call an R function using Pythonic input arguments would be great.

Answer 1

Q.1: How do I pull the various elements from the result?

Ans.1: After you run your R script:

test = ro.r(your_R_script)

You can use this code to print out all the names and values in the test object.

# iterate on names and values
# be careful output is v long
for n,v in test.items():
    print(n)
    print(v)

To list all available names , run this code:

test.names

The output:

StrVector with 12 elements.
'coeffici... 'residuals' 'effects' 'rank' ... 'xlevels' 'call'  'terms' 'model'

To print values of the 'residuals', run this:

test[test.names.index('residuals')]

Q.2: What happens to df?

Ans.2: It is still available in R environment until you delete it. You can run simple R code to check:

ro.r('''
        # View dataframe
        df
        ''')

Q.3: Is there a much much better way to do this?

Ans.3: (No answer.)