rnulltype - Converting an RPy2 ListVector to a Python dictionary

typeerror rpy2 rinterface rnulltype object is not iterable (4)

Simple R list to Python dictionary:

>>> import rpy2.robjects as robjects
>>> a = robjects.r('list(foo="barbat", fizz=123)')
>>> d = { key : a.rx2(key)[0] for key in a.names }
>>> d
{'foo': 'barbat', 'fizz': 123.0}

Arbitrary R object to Python object using R RJSONIO JSON serialization/deserialization

On R server: install.packages("RJSONIO", dependencies = TRUE)

>>> ro.r("library(RJSONIO)")
<StrVector - Python:0x300b8c0 / R:0x3fbccb0>
[str, str, str, ..., str, str, str]
>>> import rpy2.robjects as robjects
>>> rjson = robjects.r(' toJSON( list(foo="barbat", fizz=123, lst=list(33,"bb")) )  ')
>>> pyobj = json.loads( rjson[0] )
>>> pyobj
{u'lst': [33, u'bb'], u'foo': u'barbat', u'fizz': 123}
>>> pyobj['lst']
[33, u'bb']
>>> pyobj['lst'][0]
33
>>> pyobj['lst'][1]
u'bb'
>>> rjson = robjects.r(' toJSON( list(foo="barbat", fizz=123, lst=list( key1=33,key2="bb")) )  ')
>>> pyobj = json.loads( rjson[0] )
>>> pyobj
{u'lst': {u'key2': u'bb', u'key1': 33}, u'foo': u'barbat', u'fizz': 123}

The natural Python equivalent to a named list in R is a dict, but RPy2 gives you a ListVector object.

import rpy2.robjects as robjects

a = robjects.r('list(foo="barbat", fizz=123)')

At this point, a is a ListVector object.

<ListVector - Python:0x108f92a28 / R:0x7febcba86ff0>
[StrVector, FloatVector]
  foo: <class 'rpy2.robjects.vectors.StrVector'>
  <StrVector - Python:0x108f92638 / R:0x7febce0ae0d8>
[str]
  fizz: <class 'rpy2.robjects.vectors.FloatVector'>
  <FloatVector - Python:0x10ac38fc8 / R:0x7febce0ae108>
[123.000000]

What I'd like to have is something I can treat like a normal Python dictionary. My temporary hack-around is this:

def as_dict(vector):
    """Convert an RPy2 ListVector to a Python dict"""
    result = {}
    for i, name in enumerate(vector.names):
        if isinstance(vector[i], robjects.ListVector):
            result[name] = as_dict(vector[i])
        elif len(vector[i]) == 1:
            result[name] = vector[i][0]
        else:
            result[name] = vector[i]
    return result

as_dict(a)
{'foo': 'barbat', 'fizz': 123.0}

b = robjects.r('list(foo=list(bar=1, bat=c("one","two")), fizz=c(123,345))')
as_dict(b)
{'fizz': <FloatVector - Python:0x108f7e950 / R:0x7febcba86b90>
 [123.000000, 345.000000],
 'foo': {'bar': 1.0, 'bat': <StrVector - Python:0x108f7edd0 / R:0x7febcba86ea0>
  [str, str]}}

So, the question is... Is there a better way or something built into RPy2 that I should be using?

A simple function to convert nested R named lists into a nested Python dictionary :

def rext(r):
    """
    Returns a R named list as a Python dictionary
    """
    # In case `r` is not a named list
    try:
        # No more names, just return the value!
        if r.names == NULL:
            # If more than one value, return numpy array (or list)
            if len(list(r)) > 1:
                return np.array(r)
            # Just one value, return the value
            else:
                return list(r)[0]
        # Create dictionary to hold named list as key-value
        dic = {}
        for n in list(r.names):
            dic[n] = rext(r[r.names.index(n)])
        return dic
    # Uh-oh `r` is not a named list, just return `r` as is
    except:
        return r

I think to get a r vector into a dictionary does not have to be so involving, how about this:

In [290]:

dict(zip(a.names, list(a)))
Out[290]:
{'fizz': <FloatVector - Python:0x08AD50A8 / R:0x10A67DE8>
[123.000000],
 'foo': <StrVector - Python:0x08AD5030 / R:0x10B72458>
['barbat']}
In [291]:

dict(zip(a.names, map(list,list(a))))
Out[291]:
{'fizz': [123.0], 'foo': ['barbat']}

And of course, if you don't mind using pandas, it is even easier. The result will have numpy.array instead of list, but that will be OK in most cases:

In [294]:

import pandas.rpy.common as com
com.convert_robj(a)
Out[294]:
{'fizz': [123.0], 'foo': array(['barbat'], dtype=object)}

With the new version of pandas, one could also do,

import rpy2.robjects as robjects
a = robjects.r('list(foo="barbat", fizz=123)')

from rpy2.robjects import pandas2ri
print(pandas2ri.ri2py(a.names))
temp = pandas2ri.ri2py(a)
print(temp[0])
print(temp[1])