[R] converting multiple columns from POSIX* to Date

[Farrel Buchinsky]

converting a POSIX class variable to a date class is easy.
dates<-as.Date(x) #where X is of class POSIX
How does one do that to all columns in a data frame that are of POSIX
class and leave all the other columns (integers, factors) as is.

Feel free to reply with just one or two buzzwords that I could then
search for to find how to do it.

Farrel Buchinsky