Add tz support to time_trans

NEWS

@@ -1,3 +1,7 @@
+* `time_trans` gains an optional argument `tz` to specify the time zone to use
+  for the times.  If not specified, it will be guess from the first input with
+  a non-null time zone.
+
 * `date_trans` and `time_trans` now check that their inputs are of the correct
    type.  This prevents ggplot2 scales from silently giving incorrect outputs
    when given incorrect inputs.

R/trans-date.r

@@ -22,25 +22,36 @@ from_date <- function(x) {
 
 #' Transformation for times (class POSIXt).
 #'
+#' @param tz Optionally supply the time zone.  If \code{NULL}, the default,
+#'   the time zone will be extracted from first input with a non-null tz.
 #' @export
 #' @examples
 #' hours <- seq(ISOdate(2000,3,20, tz = ""), by = "hour", length.out = 10)
 #' t <- time_trans()
 #' t$trans(hours)
 #' t$inv(t$trans(hours))
 #' t$format(t$breaks(range(hours)))
-time_trans <- function() {
+time_trans <- function(tz = NULL) {
+
+  to_time <- function(x) {
+    force(x)
+    structure(x, class = c("POSIXt", "POSIXct"), tzone = tz)
+  }
+
+  from_time <- function(x) {
+    if (!inherits(x, "POSIXct")) {
+      stop("Invalid input: time_trans works with objects of class ", 
+        "POSIXct only", call. = FALSE)
+    }
+    if (is.null(tz)) {
+      tz <<- attr(as.POSIXlt(x), "tzone")[[1]]
+    }
+    structure(as.numeric(x), names = names(x))
+  }
+
   trans_new("time", "from_time", "to_time", breaks = pretty_breaks())
 }
 
-to_time <- function(x)   structure(x, class = c("POSIXt", "POSIXct"))
-from_time <- function(x) {
-  if (!inherits(x, "POSIXct")) {
-    stop("Invalid input: time_trans works with objects of class POSIXct only",
-      call. = FALSE)
-  }
-  structure(as.numeric(x), names = names(x))
-}
 
 #' Regularly spaced dates.
 #' 

inst/tests/test-trans-date.r

@@ -3,11 +3,41 @@ context("Trans - dates and times")
 a_time <- ISOdatetime(2012, 1, 1, 11, 30, 0, tz = "UTC")
 a_date <- as.Date(a_time)
 
+tz <- function(x) attr(as.POSIXlt(x), "tzone")[1]
+tz2 <- function(x) format(x, "%Z") 
+
+with_tz <- function(x, value) {
+  as.POSIXct(format(x, tz = value, usetz = TRUE), tz = value)
+}
+
 test_that("date/time scales raise error on incorrect inputs", {
   time <- time_trans()
   expect_error(time$trans(a_date), "Invalid input")
 
   date <- date_trans()
   expect_error(date$trans(a_time), "Invalid input")
 
+})
+
+test_that("time scales learn timezones", {
+  time <- time_trans()
+  x <- time$inv(time$trans(a_time))
+
+  expect_equal(tz(x), "UTC")
+  expect_equal(tz2(x), "UTC")
+
+  time <- time_trans()
+  x <- time$inv(time$trans(with_tz(a_time, "GMT")))
+
+  expect_equal(tz(x), "GMT")
+  expect_equal(tz2(x), "GMT")
+})
+
+test_that("tz arugment overrules default time zone", {
+  time <- time_trans("GMT")
+  x <- time$inv(time$trans(a_time))
+
+  expect_equal(tz(x), "GMT")
+  expect_equal(tz2(x), "GMT")
+
 })