Add figure space as style_positive option

NEWS.md

@@ -12,6 +12,10 @@
   (@teunbrand, #403).
 * The `scale_cut` argument in `number()` now works as advertised for values 
   below the lowest cut value (#346)
+* Added a new option to the `style_positive` argument in `label_*()` functions.
+  Setting this to `"space"` will add a figure space in front of the number to 
+  make it easier to align positive and negative values as figure space takes up
+  the same amount of space as `-` (#366)
 * `label_dollar()` has been superseeded by `label_currency()` for clarity (#344)
 * `sqrt_trans()` no longer returns an inverse for values outside of its domain 
   (#214)

R/label-number.R

@@ -34,6 +34,10 @@
 #'
 #'   * `"none"` (the default): no change, e.g. `1`.
 #'   * `"plus"`: preceded by `+`, e.g. `+1`.
+#'   * `"space"`: preceded by a Unicode "figure space", i.e., a space equally
+#'     as wide as a number or `+`. Compared to `"none"`, adding a figure space
+#'     can ensure numbers remain properly aligned when they are left- or
+#'     right-justified.
 #' @param style_negative A string that determines the style of negative numbers:
 #'
 #'   * `"hyphen"` (the default): preceded by a standard hypen `-`, e.g. `-1`.
@@ -103,7 +107,7 @@
 #' demo_continuous(c(0, 100), labels = label_number(suffix = "\u00b0C"))
 label_number <- function(accuracy = NULL, scale = 1, prefix = "",
                          suffix = "", big.mark = " ", decimal.mark = ".",
-                         style_positive = c("none", "plus"),
+                         style_positive = c("none", "plus", "space"),
                          style_negative = c("hyphen", "minus", "parens"),
                          scale_cut = NULL,
                          trim = TRUE, ...) {
@@ -219,7 +223,7 @@ comma_format <- label_comma
 #' @return A character vector of `length(x)`.
 number <- function(x, accuracy = NULL, scale = 1, prefix = "",
                    suffix = "", big.mark = " ", decimal.mark = ".",
-                   style_positive = c("none", "plus"),
+                   style_positive = c("none", "plus", "space"),
                    style_negative = c("hyphen", "minus", "parens"),
                    scale_cut = NULL,
                    trim = TRUE, ...) {
@@ -280,6 +284,8 @@ number <- function(x, accuracy = NULL, scale = 1, prefix = "",
   }
   if (style_positive == "plus") {
     ret[sign > 0] <- paste0("+", ret[sign > 0])
+  } else if (style_positive == "space") {
+    ret[sign > 0] <- paste0("\u2007", ret[sign > 0])
   }
 
   # restore NAs from input vector