jonkeane commented on a change in pull request #12506:
URL: https://github.com/apache/arrow/pull/12506#discussion_r833487664
##########
File path: r/R/dplyr-funcs-datetime.R
##########
@@ -189,6 +189,65 @@ register_bindings_datetime <- function() {
})
}
+register_bindings_duration <- function() {
+ register_binding("difftime", function(time1,
+ time2,
+ tz,
+ units = c("auto", "secs", "mins",
+ "hours", "days", "weeks")) {
+ units <- match.arg(units)
+ if (units != "secs") {
+ abort("`difftime()` with units other than seconds not supported in
Arrow")
+ }
+
+ if (!missing(tz)) {
+ warn("`tz` is an optional argument to `difftime()` in R and will not be
used in Arrow")
+ }
+
+ time1 <- build_expr("cast", time1, options = cast_options(to_type =
timestamp()))
+ time2 <- build_expr("cast", time2, options = cast_options(to_type =
timestamp()))
+
+ build_expr("cast", time1 - time2, options = cast_options(to_type =
duration("s")))
+ })
+
+ register_binding("as.difftime", function(x,
+ format = "%X",
+ units = "auto") {
+ # windows doesn't seem to like "%X"
+ if (format == "%X" & tolower(Sys.info()[["sysname"]]) == "windows") {
+ format <- "%H:%M:%S"
+ }
+
+ if (units != "secs") {
+ abort("`as.difftime()` with units other than seconds not supported in
Arrow")
+ }
+
+ if (call_binding("is.character", x)) {
+ x <- build_expr("strptime", x, options = list(format = format, unit =
0L))
+ y <- build_expr("strptime", "0:0:0", options = list(format = "%H:%M:%S",
unit = 0L))
+ diff_x_y <- call_binding("difftime", x, y, units = "secs")
+ return(diff_x_y)
+ }
Review comment:
Have you seen
https://issues.apache.org/jira/browse/ARROW-15996?focusedCommentId=17511259&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-17511259
?
Would the following work?
```
# strptime, convert to time64
x <- build_expr("strptime", x, options = list(format = format, unit =
0L))$cast(time64("us"))
# Complex casting only due to cast type restrictions: time64 -> int64 ->
duration(us) -> duration(s)
x <- x$cast(int64())$cast(duration("us"))$cast(duration("s"))
```
Yes, it does involve a series of casts (though most of those should be
pretty cheap since it's mostly integers being moved around.
The nice thing about this is that it's conceptually isolated: going from a
"%H:%M:%S" to a time64 to a duration. Where as (3) requires a few assumptions
about how `strptime()` fills in date details (if you check this it's actually
totally different in Arrow and R!) and then discards them. And agree that (1)
is not ideal: `difftime` in R is definitely more like Arrow's `duration` than
`time32|64()` objects.
And there are a number of ways this sequence of casts could be simplified
(all the examples below use the array: `arr <- Array$create("01:00:00")`)
either in ARROW-15996 or elsewhere:
* being able to go from `time64` to `duration` directly:
`call_function("strptime", arr, options = list(format = "%H:%M:%S", unit
= 0L))$cast(time64("us"))$cast(duration("s"))`
* being able to go from `int32` to duration, then we could do something
like:
`call_function("strptime", arr, options = list(format = "%H:%M:%S", unit
= 0L))$cast(time32("s"))$cast(int32())$cast(duration("s"))`
* Probably a few more...
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