[R] vector of dates

[Barbara.Rogo at uniroma1.it]

   I have to construct a vector of date with a cycle "for". I use the function
   "seq", but when I allocate in a vector, this becomes a number!!!
   How do I have? thank you
   Example:
   dataval=as.Date("2011/07/01")
   date_val=seq(dataval,length=260,by="-7 day")
   date_inizio=c()
   date_condizione=c()
   for (k in 1:length(date_val)){
       date_inizio[k]=seq(date_val[k],length=2,by="-5 years")[2]
       date_condizione[k]=seq(date_val[k],length=2,by="-2 years")[2]
       }