How to prevent write.csv from changing POSIXct, dates and times class back to character/factors?

Question

I have a .csv file with one field each for datetime, date and time. Originally they are all character fields and I have converted them accordingly. At the end of my code, if

Answer 1

If you want to preserve all of the time information so it can be read in again, this recipe should work:

dat <- data.frame(time=as.POSIXlt("2013-04-25 09:00 BST"), quantity=1)
dat2 <- dat
dat2$time <- format(dat2$time, usetz=TRUE)
write.csv(dat2, "time.csv", row.names=FALSE)

It gives the following CSV file:

"time","quantity"
"2013-04-25 09:00:00 BST",1

in which the timezone information is presented explicitly; if you apply write.csv to the original dat, the formatting is lost.