Converting character to POSIXct in R loses time zone

Question

I am trying to convert a character string into a POSIXct date format and running into a problem with the time zone information.

The original character data looks like this:

SD$BGN_DTTM
[1] "1956-05-25 14:30:00 CST" "1956-06-05 16:30:00 CST" "1956-07-04 15:30:00 CST"
[4] "1956-07-08 08:00:00 CST" "1956-08-19 12:00:00 CST" "1956-12-23 00:50:00 CST"

but when I attempt to convert using as.POSIXct , this happens:

SD$BGN_DTTM <- as.POSIXct(SD$BGN_DTTM)
[1] "1956-05-25 14:30:00 PDT" "1956-06-05 16:30:00 PDT" "1956-07-04 15:30:00 PDT"
[4] "1956-07-08 08:00:00 PDT" "1956-08-19 12:00:00 PDT" "1956-12-23 00:50:00 PST"

It looks like the function isn't reading the time zone I've specified. Since my computer is on PDT, it looks like it has used that instead. Note also that it has appended PST to the last date (seems odd). Can anyone tell me what is going on here, and whether there is a method to get R to read the time zone information as shown?

Answer 1

This would still have the problem you noticed with daylight/standard times:

> strptime(test, format="%Y-%m-%d %H:%M:%S", tz="America/Chicago")
[1] "1956-05-25 14:30:00 CDT" "1956-06-05 16:30:00 CDT"
[3] "1956-07-04 15:30:00 CDT" "1956-07-08 08:00:00 CDT"
[5] "1956-08-19 12:00:00 CDT" "1956-12-23 00:50:00 CST"

The strptime function refuses to honor the "%Z" format for input (which in its defense is documented.) Many people have lost great gobs of hair and probably some keyboards into monitors in efforts to get R timezones working to their (dis?)satisfaction.