IDateTime fails on POSIXct without tzone.

[lbilli]

The function IDateTime generates an error when applied to POSIXct values without tzone attribute:

library(data.table)
IDateTime(Sys.time())
# Error in if (tz == "UTC") { : argument is of length zero

Versions
R: 3.3.2
data.table: 1.10.0 and latest 1.10.1

[lbilli]

Some more insights.

library(data.table)
x <- Sys.time()

attr(x, "tzone")
# NULL

IDateTime(x)
# Error in if (tz == "UTC") { : argument is of length zero

However, curiously this works as expected:

data.table(idate = as.IDate(x), itime = as.ITime(x))
#         idate    itime
# 1: 2017-03-14 09:27:09

There's no issue if x has a tzone attribute (even if it's an empty string):

x <- as.POSIXct("2017-03-14 09:16:14")

attr(x, "tzone")
# [1] ""

IDateTime(x)
#         idate    itime
# 1: 2017-03-14 09:16:14

This issue is still present with these versions:
R: 3.3.3
data.table: 1.10.4

[MichaelChirico]

This almost feels like an R bug more than a data.table bug.

It seems like by default a POSIXct object is supposed to have non-NULL "tzone" attribute:

attr(as.POSIXct('2017-03-17 00:00:00'), 'tzone')
#[1] ""

But this isn't the case for Sys.time():

attr(Sys.time(), 'tzone')
# NULL

And in fact strptime suggests a NULL tz value is illegal:

as.POSIXct('2017-03-17 00:00:00', tz = NULL)

Error in strptime(xx, f <- "%Y-%m-%d %H:%M:%OS", tz = tz) :
invalid tz value

There's something going on with lazy evaluation that's causing the discrepancy between

IDateTime(Sys.time())

Error in if (tz == "UTC") { : argument is of length zero

and

x = Sys.time()
data.table(idate = as.IDate(x), itime = as.ITime(x))
#         idate    itime
# 1: 2017-03-17 16:28:10

(this is an unexpected error because IDateTime.default is precisely the above):

data.table:::IDateTime.default
# function (x, ...) 
# {
#     data.table(idate = as.IDate(x), itime = as.ITime(x))
# }

Due to lazy evaluation, x is unevaluated when it gets passed to as.IDate, and hence gets sent to as.IDate.default, whereas for IDateTime(Sys.time()), Sys.time() has been evaluated before being passed to as.IDate, so it gets sent to as.IDate.POSIXct. as.Date(x, ...) excludes the tz argument, so it picks up the default of "UTC".