DOC: Complete R interface section

[sinhrks]

Currently, "rpy2 R interface" documentation has blank section. Added descriptions to cover required basic topics.

[jorisvandenbossche]

@sinhrks Great to work on this! (it was a little bit a stub page now)

But I am not sure of the current status of how the conversion should be preferably done. Eg see http://stackoverflow.com/questions/20630121/pandas-how-to-convert-r-dataframe-back-to-pandas, I don't know if convert_to_r_dataframe is still needed (with the newer rpy2)

[sinhrks]

Thanks. I've used rpy 2.3.8 and will check 2.4.0 spec.

[jorisvandenbossche]

If I look at the rpy2 docs, it seems this conversion machinery pandas2ri was already there from 2.3.3, although there were some changes in 2.4

[jreback]

@jorisvandenbossche I am ok with this

[sinhrks]

I've briefly checked pandas2ri of rpy2.4.0, and found current pandas conversion looks better. pandas2ri doesn't convert returned rpy2 DataFrame automatically, and may raise ValueError for DatetimeIndex.

But it is good if we don't have to care about rpy2 instances. I think it can be achieved by simple wrapper on pandas.rpy2.common, and will issue a PR for this.

import pandas as pd
import pandas.rpy.common as com
import rpy2.robjects as ro
from rpy2.robjects import pandas2ri

pandas2ri.activate()

iris = com.load_data('iris')
ro.r.assign('iris', iris)
returned = ro.r['iris']
type(returned)
# <class 'rpy2.robjects.vectors.DataFrame'>

df = pd.DataFrame(np.random.randn(20, 5),
                  index=pd.date_range(start='2011/01/01', freq='D', periods=20))
ro.r.assign('df', df)
returned = ro.r['df']
# ValueError: Unknown numpy array type.

[jorisvandenbossche]

Something else, but maybe somewhat orthogonal to this PR, I think we could also mention the IPython rmagic in this doc page.

[davclark]

Note rpy2 2.4+ is now the blessed "proper" location to get the rmagic via:

%load_ext rpy2.ipython

The updated rmagic lives in that sub-package in rpy2.

[jreback]

@jorisvandenbossche merge when happy with this

[jorisvandenbossche]

'Below example shows how to retrieve ...' + 'vecrtor' -> 'vector'

[jorisvandenbossche]

I think it depends a bit on the outcome of #7385?

[jreback]

@sinhrks ok, deferring this to outcome of #7385

or if you want to document the current, then you can change (or submit a new one).

[jreback]

let's redirect to rpy2 for conversions, see #9602