[R] Object and file sizes

[Göran Broström]

Hello,

I have two large data frames, 'liss' (170 million obs, 8 variables) and 
'fobb' (52 million obs, 8 variables, same as for 'liss'), and checking 
their sizes I get

 > object.size(liss)
7477492552 bytes
 > object.size(fobb)
2494591736 bytes

Fair enough, but when I save them to disk (saveRDS), the size relation 
is reversed: 'fobb.rds' takes up 273 MB while 'liss.rds' uses 146 MB!

I was puzzled by this and thought that I had made a mistake in creating 
them, but the only explanation I can find for this is that 'liss' 
contains a lot more missing values.

Suggestions?

Thanks, Göran