thisisnic commented on a change in pull request #12154:
URL: https://github.com/apache/arrow/pull/12154#discussion_r785872219
##########
File path: r/R/util.R
##########
@@ -209,3 +209,74 @@ handle_csv_read_error <- function(e, schema) {
abort(e)
}
+
+
+parse_period_unit <- function(x) {
+
+ # the regexp matches against fractional units, but per lubridate
+ # supports integer multiples of a known unit only
+ match_info <- regexpr(
+ pattern = " *(?<multiple>[0-9.,]+)? *(?<unit>[^ \t\n]+)",
+ text = x[[1]],
+ perl = TRUE
+ )
+
+ capture_start <- attr(match_info, "capture.start")
+ capture_length <- attr(match_info, "capture.length")
+ capture_end <- capture_start + capture_length - 1L
+
+ str_unit <- substr(x, capture_start[[2]], capture_end[[2]])
+ str_multiple <- substr(x, capture_start[[1]], capture_end[[1]])
+
+ known_units <- c("nanosecond", "microsecond", "millisecond", "second",
+ "minute", "hour", "day", "week", "month", "quarter", "year")
+
+ # match the period unit
+ str_unit_start <- substr(str_unit, 1, 3)
+ unit <- as.integer(pmatch(str_unit_start, known_units)) - 1L
+
+ if(any(is.na(unit))) {
+ abort(sprintf("Unknown unit '%s'", str_unit))
+ }
+
+ # empty string in multiple interpreted as 1
+ if(capture_length[[1]] == 0) {
+ multiple <- 1L
+
+ } else {
+
+ # special cases: interpret fractions of 1 second as integer
+ # multiples of nanoseconds, microseconds, or milliseconds
+ # to mirror lubridate syntax
+ multiple <- as.numeric(str_multiple)
+
+ if(unit == 3L & multiple < 10^-6) {
+ unit <- 0L
+ multiple <- 10^9 * multiple
+ }
+ if(unit == 3L & multiple < 10^-3) {
+ unit <- 1L
+ multiple <- 10^6 * multiple
+ }
+ if(unit == 3L & multiple < 1) {
+ unit <- 2L
+ multiple <- 10^3 * multiple
+ }
+
+ multiple <- as.integer(multiple)
+ }
+
+ # more special cases: lubridate imposes sensible maximum
+ # values on the number of seconds, minutes and hours
+ if(unit == 3L & multiple > 60) {
+ abort("Rounding with second > 60 is not supported")
+ }
Review comment:
Sounds good!
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