Vadim Ogranovich <vograno <at> evafunds.com> writes: : : Hi, : : As far as I can tell data.frame class adds two features to those of : lists: : * matrix structure via [,] and [,]<- operators (well, I know these are : actually "["(i, j, ...), not "[,]"). : * row names attribute. : : It seems that the overhead of the support for the row names, both : computational and RAM-wise, is rather non-trivial. I frequently : subscript from a data.frame, i.e. use [,] on data frames, and my timing : shows that the equivalent list operation is about 7 times faster, see : below. : : On the other hand, at least in my usage pattern, I really rarely benefit : from the row names attribute, so as far as I am concerned row names is : just an overhead. (Of course the speed difference may be due to other : factors, the only thing I can tell is that subscripting is very slow in : data frames relative to in lists). : : I thought of writing a new class, say lightweight.data.frame, that would : be polymorphic with the existing data.frame class. The class would : inherit from "list" and implement [,], [,]<- operators. It would also : implement the "rownames" function that would return seq(nrow(x)), etc. : It should also implement as.data.frame to avoid the overhead of : conversion to a full-blown data.frame in calls like lm(y ~ x, : data=myLightweightDataframe).
The next version of zoo (currently in test) supports lists in the data argument of lm and can also merge zoo series into a list (or to another zoo series, as it does now). Would that be a sufficient alternative? ______________________________________________ [EMAIL PROTECTED] mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
