Change leading characters in label_date_short() (#456)

NEWS.md

@@ -1,5 +1,6 @@
 # scales (development version)
 
+* New `label_date_short(leading)` argument to replace leading zeroes (#442)
 * `breaks_pretty()` will return the input limit when it has no range (#446)
 * `transform_exp()` now has more sensible breaks, available in `breaks_exp()` 
   (@teunbrand, #405).

R/label-date.R

@@ -22,6 +22,8 @@
 #'   uses the current locale. Setting this argument requires stringi, and you
 #'   can see a complete list of supported locales with
 #'   [stringi::stri_locale_list()].
+#' @param leading A string to replace leading zeroes with. Can be `""` to
+#'   disable leading characters or `"\u2007"` for figure-spaces.
 #' @export
 #' @examples
 #' date_range <- function(start, days) {
@@ -53,8 +55,9 @@ label_date <- function(format = "%Y-%m-%d", tz = "UTC", locale = NULL) {
 #' @export
 #' @rdname label_date
 #' @param sep Separator to use when combining date formats into a single string.
-label_date_short <- function(format = c("%Y", "%b", "%d", "%H:%M"), sep = "\n") {
-  force_all(format, sep)
+label_date_short <- function(format = c("%Y", "%b", "%d", "%H:%M"), sep = "\n",
+                             leading = "0") {
+  force_all(format, sep, leading)
 
   function(x) {
     dt <- unclass(as.POSIXlt(x))
@@ -90,7 +93,16 @@ label_date_short <- function(format = c("%Y", "%b", "%d", "%H:%M"), sep = "\n")
     )
 
     format <- apply(for_mat, 1, function(x) paste(rev(x[!is.na(x)]), collapse = sep))
-    format(x, format)
+    x <- format(x, format)
+
+    if (isTRUE(leading == "0")) {
+      return(x)
+    }
+
+    # Replace leading 0s with `leading` character
+    x <- gsub("^0", leading, x)
+    x <- gsub(paste0(sep, "0"), paste0(sep, leading), x, fixed = TRUE)
+    x
   }
 }
 

tests/testthat/test-label-date.R

@@ -24,6 +24,15 @@ test_that("can set locale", {
   expect_equal(time_format("%B", locale = "fr")(x), "janvier")
 })
 
+test_that("label_date_short can replace leading zeroes", {
+  x <- seq(as.Date("2024-01-01"),  as.Date("2025-01-01"), by = "1 month")
+  labels <- label_date_short(
+    format = c("%Y", "%m", "%d"),
+    sep = "-", leading = "x"
+  )(x)
+  expect_equal(labels, c("x1-2024", paste0("x", 2:9), c(10:12), "x1-2025"))
+})
+
 test_that("date_short doesn't change unexpectedly", {
   expect_snapshot({
     dformat <- label_date_short()