nealrichardson commented on a change in pull request #10507:
URL: https://github.com/apache/arrow/pull/10507#discussion_r656448695
##########
File path: r/R/dplyr-functions.R
##########
@@ -442,3 +442,74 @@ nse_funcs$strptime <- function(x, format = "%Y-%m-%d
%H:%M:%S", tz = NULL, unit
Expression$create("strptime", x, options = list(format = format, unit =
unit))
}
+
+nse_funcs$second <- function(x) {
+ Expression$create("add", Expression$create("second", x),
Expression$create("subsecond", x))
+}
+
+# After ARROW-13054 is completed, we can refactor this for simplicity
+#
+# Arrow's `day_of_week` kernel counts from 0 (Monday) to 6 (Sunday), whereas
+# `lubridate::wday` counts from 1 to 7, and allows users to specify which day
+# of the week is first (Sunday by default). This Expression converts the
returned
+# day of the week back to the value that would be returned by lubridate by
+# providing offset values based on the specified week_start day, and adding 1
+# so the returned value is 1-indexed instead of 0-indexed.
+#
+# This looks complex but if you look at the lubridate implementation of wday,
+# you can see that this is the same maths, but with 1 added at the end to
+# account for the fact that R is 1-based and the Arrow implementation is
0-based
+#
+# overall formula to convert from arrow::wday to lubridate::wday is:
+# (3 +wday(day) + (5 - start)) %% 7) + 1
+#
+# To calculate e1 %% e2, we can rearrange it as:
+# {e1 - e2 * ( e1 %/% e2 )}
+#
+# And e1 %/% e2 can itself be done via casting e1/e2 to an integer
+nse_funcs$wday <- function(x, label = FALSE, abbr = TRUE, week_start =
getOption("lubridate.week.start", 7)) {
+ if (label) {
+ arrow_not_supported("Label argument")
+ }
+
+ # e1 = 3 +wday(day) + (5 - start)
+ e1 = Expression$create(
+ "add_checked",
+ # 3 + wday(date)
+ Expression$create("add_checked",
+ Expression$scalar(3),
+ Expression$create("day_of_week", x)
+ ),
+ # (5 - start)
+ Expression$create("subtract_checked",
+ Expression$scalar(5),
+ Expression$scalar(week_start)
+ )
+ )
+
+ e2 = Expression$scalar(7)
+
+ # (e1 - e2 * ( e1 %/% e2 )) + 1
+ Expression$create(
+ "add_checked",
+ Expression$scalar(1),
+ # e1 - e2 * ( e1 %/% e2 )
+ Expression$create(
+ "subtract_checked",
+ # e1
+ e1,
+ # e2 * ( e1 %/% e2 )
+ Expression$create("multiply_checked",
+ e2,
+ # e1 %/% e2; because as.integer(x/y) == x%/%y
+ Expression$create(
+ "cast",
+ Expression$create("divide_checked", e1, e2),
+ options = cast_options(to_type = int32(), allow_float_truncate =
TRUE,
Review comment:
If you make all of the scalars integers (e.g. 1L), do you still need to
cast?
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