Date and datetime columns become numeric on round-trip

[warnes]

Date and datetime columns written using write.xport and read back in using read.xport are losing the date and time type information:

Running tests/testDates.R yields:

> library(SASxport)

> Sys.setenv("TZ"="GMT")

> ## Create a small data set containing dates, times, and date-times
> 
> dates <- c("02/27/92", "02/27/92", "01/14/92", "02/28/92", "02/01/92")

> times <- c("23:03:20", "22:29:56", "01:03:30", "18:21:03", "16:56:26")

> temp <- data.frame(
+   x=c(1, 2, 3, 4, 5 ),
+   y=c('a', 'B', 'c', 'd', 'e' ),
+   dates=strptime(dates, "%m/%d/%y"),
+   datetimes=strptime( paste .... [TRUNCATED] 

> print(temp)
  x y      dates           datetimes
1 1 a 1992-02-27 1992-02-27 23:03:20
2 2 B 1992-02-27 1992-02-27 22:29:56
3 3 c 1992-01-14 1992-01-14 01:03:30
4 4 d 1992-02-28 1992-02-28 18:21:03
5 5 e 1992-02-01 1992-02-01 16:56:26

> write.xport( DATETIME=temp, file="datetime.xpt")

> temp2 <- read.xport(file="datetime.xpt", names.tolower=FALSE)

> #! FIXME: Date and datetime are coming back as numeric
> print(temp2)
  X Y      DATES   DATETIME
1 1 a 1014768000 1014851000
2 2 B 1014768000 1014848996
3 3 c 1010966400 1010970210
4 4 d 1014854400 1014920463
5 5 e 1012521600 1012582586

> identical(temp, temp2)
[1] FALSE

> # Test for issue #19: toSAS() - The number of seconds since
> # 1960-01-01:00:00:00 GMT is greater than it is supposed to be
> 
> zeroDate <- ISOdat .... [TRUNCATED] 

> zeroSAS <- toSAS(zeroDate, format="DATETIME19.")

> stopifnot(zeroSAS==0)