Develope interface to rpy2 for iris

[cpelley]

Requirement: Convert between iris cubes/coordinates and 'r' data types.
https://github.com/cpelley/iris/tree/rpy2_interface

Background:
http://www.statmethods.net/input/datatypes.html
http://en.wikibooks.org/wiki/R_Programming/Data_types
http://rpy.sourceforge.net/rpy2_documentation.html

Suitable objects for cube translation (minimum loss of metadata):
DataFrames, Matrices, Arrays?
All three can have row-column labels which could be associated with dim coordinates)

numeric/character/logical vector
Matrices - All columns in a matrix must have the same mode(numeric, character, etc.) and the same length.
Arrays - Arrays are similar to matrices but can have more than two dimensions.
DataFrames - A data frame is more general than a matrix, in that different columns can have different modes (numeric, character, factor, etc.).
Lists - An ordered collection of objects (components). A list allows you to gather a variety of (possibly unrelated) objects under one name.

Matrices/arrays/dataframes: cube representation in its simplest single object form.
Lists: cube representation with the possibility of maintaining more metadata.

[cpelley]

Additional points:

1. Handling dates by mean of setting appropriate strings which represent dates.
2. Handling missing data.