Allow subsecond intervals with date_breaks() (#160)

* Add subsecond interval support to date_breaks() and full_seq()

Closes #85 

* Fix tz mismatch for sec and min intervals. Fix tests.

NEWS.md

@@ -1,5 +1,7 @@
 # scales 0.5.0.9000
 
+* `date_breaks()` now supports subsecond intervals (@dpseidel, #85).
+
 * New function `modulus_trans()` implements the modulus transformation for positive
   and negative values (@dpseidel).
 

R/date-time.r

@@ -13,10 +13,14 @@ floor_date <- function(date, time) {
     as.Date(cut(date, time, right = TRUE, include.lowest = TRUE))
   }
 }
+
 floor_time <- function(date, time) {
   to_time <- function(x) {
     force(x)
-    structure(x, class = c("POSIXt", "POSIXct"))
+    structure(x,
+      class = c("POSIXt", "POSIXct"),
+      tzone = attr(date, "tzone", exact = TRUE) %||% ""
+    )
   }
 
   prec <- parse_unit_spec(time)

R/full-seq.r

@@ -33,5 +33,13 @@ fullseq.Date <- function(range, size, ...) {
 }
 #' @export
 fullseq.POSIXt <- function(range, size, ...) {
-  seq(floor_time(range[1], size), ceiling_time(range[2], size), by = size)
+
+  # for subsecond interval support
+  # seq() does not support partial secs in character strings
+  parsed <- parse_unit_spec(size)
+  if (parsed$unit == "sec") {
+    seq(floor_time(range[1], size), ceiling_time(range[2], size), by = parsed$mult)
+  } else {
+    seq(floor_time(range[1], size), ceiling_time(range[2], size), by = size)
+  }
 }

R/trans-date.r

@@ -107,7 +107,7 @@ time_breaks <- function(n = 5) {
 #'
 #' @param width an interval specification, one of "sec", "min", "hour",
 #'   "day", "week", "month", "year". Can be by an integer and a space, or
-#'   followed by "s".
+#'   followed by "s". Fractional seconds are supported.
 #' @export
 date_breaks <- function(width = "1 month") {
   force(width)

tests/testthat/test-trans-date.r

@@ -40,3 +40,22 @@ test_that("tz arugment overrules default time zone", {
   expect_equal(tz(x), "GMT")
   expect_equal(tz2(x), "GMT")
 })
+
+test_that("date_breaks() works", {
+  times <- as.POSIXct(c("2000-01-01 08:29:58", "2000-01-01 08:30:10"), tz = "UTC")
+
+  expect_equal(
+    date_breaks("1 hour")(times),
+    as.POSIXct(c("2000-01-01 8:00:00 UTC", "2000-01-01 9:00:00 UTC"), tz = "UTC")
+  )
+  expect_equal(
+    date_breaks(".5 secs")(times)[1:2],
+    as.POSIXct(c("2000-01-01 08:29:58.0 UTC", "2000-01-01 08:29:58.5 UTC"), tz = "UTC")
+  )
+
+  dates <- a_date + 1:30
+  expect_equal(
+    date_breaks("1 month")(dates),
+    as.Date(c("2012-01-01", "2012-02-01"))
+  )
+})