Is it possible to pass dataframes between R and Python using Arrow with zero-copy? Arrow is an in-memory format, so I can have a dataframe in Python backed by the arrow format. So the dataframe sits in memory, can I use that dataframe directly from R without making a copy of the dataframe? Imagine if the dataframe is 100G in size so copying is very inefficient.

I read in the documentation of Arrow that there is zero-copy streaming, but there isn't a way to make the whole dataframe available.
Not currently, though hopefully very soon. https://issues.apache.org/jira/browse/ARROW-3750 is in progress and hopefully will resolve in the coming weeks.