[R] sparse data frame (crsp?)

[ivo_welch-rstat8303@mailblocks.com]

dear R wizards:  does R have the facilities to handle sparse data 
frames?  I am thinking of reading a data base like the daily CRSP data 
into R, observations being firms, columns being days, data being stock 
returns.  but this will only fit into my memory if I can convince R to 
not have to store missing observations, and to return NA upon read 
access to missing observations.  pointers appreciated.  sincerely,  /iaw