"Warnes, Gregory R" <[EMAIL PROTECTED]> writes: > > -----Original Message----- > > From: Luke Tierney [mailto:[EMAIL PROTECTED]] > > > R does not provide a pairlist data structure. This creates a dilemma > > when translating some list-based xlispstat code, or, more > > importantly, when implementing an algorithm for which parilists are > > the natural data structure to use. > > ... > > Pairlists were and still are used internally for many things. > > ... > > Wouldn't it, therefore, make sense to provide a 'pairlist' package which > exposes the internal pairlist structure and provides appropriate functions > (car, cdr, ...), instead of expecting people to keep re-implementing these > features?
Some ancient consideration pops up here. We do actually expose pairlists in a few places (try mode(.Options)). Some people consider that this is a remnant and should be stamped out, but we might also consider doing what you suggest. The big problem with old R was not so much the pairlists but that they were used for representing objects of mode "list" so to get to X[[n]] you had to count through the list from the beginning which killed performance in some important cases. Then again, adding elements to a generic vector requires copying the whole thing. Of course all the legacy S code tended to do the former and not the latter, so generic vectors ended up winning. One or two reservations: With full lisp style access, could we end up with (circular) data structures that confuse the garbage collector? And might we -- supposing we allowed destructive list modifications -- end up with strange semantics a la the .Alias mess we had for a while? Of course Luke would be the first to know about this. Then of course there is the question of reverse compatibility. I don't consider it much of a loss if R code doesn't run in Splus, but others might. -- O__ ---- Peter Dalgaard Blegdamsvej 3 c/ /'_ --- Dept. of Biostatistics 2200 Cph. N (*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918 ~~~~~~~~~~ - ([EMAIL PROTECTED]) FAX: (+45) 35327907 ______________________________________________ [EMAIL PROTECTED] mailing list http://www.stat.math.ethz.ch/mailman/listinfo/r-help
