sqldf: Changes timestamp from localtime to GMT/UTC

Question

On my machine, sqldf changes a POSIXct from localtime(I'm at CST, GMT -0600) to GMT/UTC. Is this expected behavior? Can I stop R or sqldf from doing this? Here is my code:

> library('sqldf')
> 
> before <- data.frame(ct_sys = Sys.time())
> before
               ct_sys
1 2012-03-01 12:57:58
> after <- sqldf('select * from before')
> after
               ct_sys
1 2012-03-01 18:57:58
> 

Answer 1

That seems to be a time zone bug in sqldf. It should be fixed now in sqldf version 0.4-6.2 (not yet on CRAN but you can try it out like this):

library(sqldf)
source("http://sqldf.googlecode.com/svn/trunk/R/sqldf.R")
before <- data.frame(ct_sys = Sys.time()); before
after <- sqldf('select * from before'); after

Even without doing that sqldf("select * from before", method = "raw") will work although that will return a numeric column (which you can convert to POSIXct) and may affect other columns too. Here is an example of using method = "raw". Note that in both cases we get 1330661786.181:

> library(sqldf)
>
> before <- data.frame(ct_sys = Sys.time()); dput(before)
structure(list(ct_sys = structure(1330661786.181, class = c("POSIXct", 
"POSIXt"))), .Names = "ct_sys", row.names = c(NA, -1L), class = "data.frame")
>
> after <- sqldf('select * from before', method = "raw"); dput(after)
structure(list(ct_sys = 1330661786.181), .Names = "ct_sys", row.names = 1L, class = "data.frame")

EDIT: added example of using method = "raw"