title: Can you "tie", or provide an alternative implementation, of a data.frame in R?
body: <p>In Perl (and probably other langauges), you can "tie" a variable to replace it's built-in behavior with user-defined behavior.  For example, a hash table can be tied with custom "get" and "fetch" subroutines which, for example, query BerkeleyDB so that data is persistent and not limited by RAM, but still looks and acts like regular hash to Perl.</p>
  
  <p>Is something similar possible with R?  In particular, I was thinking, since a <code>data.frame</code> looks much like a table in a relational db, that if a <code>data.frame</code> were tied to something like SQLite, it would enable R to handle very large data frames (I've stuffed 100GB+ into SQLite) without any code changes.</p>