jorisvandenbossche commented on code in PR #35671:
URL: https://github.com/apache/arrow/pull/35671#discussion_r1203809343
##########
r/R/dplyr-funcs-datetime.R:
##########
@@ -61,12 +61,14 @@ register_bindings_datetime_utility <- function() {
tz <- Sys.timezone()
}
- # if a timestamp does not contain timezone information (i.e. it is
+ # If a timestamp does not contain timezone information (i.e. it is
# "timezone-naive") we can attach timezone information (i.e. convert it
into
# a "timezone-aware" timestamp) with `assume_timezone`
# if we want to cast to a different timezone, we can only do it for
- # timezone-aware timestamps, not for timezone-naive ones
- if (!is.null(tz)) {
+ # timezone-aware timestamps, not for timezone-naive ones.
+ # strptime in Acero will return a timezone-aware timestamp if %z is
+ # part of the format string.
+ if (!is.null(tz) && !grepl("%z", format, fixed = TRUE)) {
Review Comment:
I don't understand how timezones work in R (and with POSIXlt and POSIXct),
but with the above change, the `tz` keyword will just be ignored when the
string includes an offset?
That doesn't match fully what base R does:
```
> strptime("2020-05-01T00:00+0100", format="%Y-%m-%dT%H:%M%z")
[1] "2020-05-01 01:00:00"
> strptime("2020-05-01T00:00+0100", format="%Y-%m-%dT%H:%M%z",
tz="US/Eastern")
[1] "2020-04-30 19:00:00"
```
(but again, I don't really know how to interpret those returned values, and
whether they are tz "aware" or "native" or even if those concepts even exist in
R. I looked at the `$zone` and `$gmtoff` attributes of the above return values,
but can't make sense of it)
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