[R] Basic date time arithmetics operations

[Fan]

Hello,

For basic date time arithmetics operations, AFAK, there're 
actually the function difftime() and the (dt + num) operations.

I'm wondering if other basic operations exist, like
add(dt, num, unit) where unit would be "y", "q", "m", etc. 

Also for the function seq.dates (or seq.POSIXt), the 
case for by="months" would be more useful if it takes
the situation of the end of month into account. 
For example,

> seq(ISOdate(2002,1,31), by="months", length=3)

"2002-01-31 13:00:00 CET" 
"2002-03-03 13:00:00 CET" 
"2002-03-31 13:00:00 CET"

rather than

"2002-01-31 13:00:00 CET" 
"2002-02-28 13:00:00 CET" 
"2002-03-31 13:00:00 CET"

Thanks
--
Fan

************ VITE, C'EST LE MOMENT DE VOUS ABONNER A L'ADSL !!! **********
Du 3 avril au 5 mai, série limitée ADSL 128K, cliquez vite ici : http://register.tiscali.fr/adsl/ 
Offre promotionnelle soumise à conditions, réservée aux nouveaux abonnés ADSL Tiscali.