Adjust expand_range() so zero range scales respect mul and add (#161)

fixes tidyverse/ggplot2#2281

NEWS.md

@@ -1,5 +1,8 @@
 # scales 0.5.0.9000
 
+* `expand_range()` arguments `mul` and `add` now affect scales with a range of 0
+   (@dpseidel, tidyverse/ggplot2#2281).
+
 * `date_breaks()` now supports subsecond intervals (@dpseidel, #85).
 
 * New function `modulus_trans()` implements the modulus transformation for positive

R/bounds.r

@@ -223,15 +223,12 @@ squish_infinite <- function(x, range = c(0, 1)) {
 #' @param add additive constant
 #' @param zero_width distance to use if range has zero width
 #' @export
-
 expand_range <- function(range, mul = 0, add = 0, zero_width = 1) {
   if (is.null(range)) return()
 
-  if (zero_range(range)) {
-    c(range[1] - zero_width / 2, range[1] + zero_width / 2)
-  } else {
-    range + c(-1, 1) * (diff(range) * mul + add)
-  }
+  width <- if (zero_range(range)) zero_width else diff(range)
+
+  range + c(-1, 1) * (width * mul + add)
 }
 
 #' Determine if range of vector is close to zero, with a specified tolerance

tests/testthat/test-bounds.r

@@ -79,3 +79,10 @@ test_that("scaling is possible with logical values", {
   expect_equal(rescale(c(FALSE, TRUE)), c(0, 1))
   expect_equal(rescale_mid(c(FALSE, TRUE), mid = 0.5), c(0, 1))
 })
+
+test_that("expand_range respects mul and add values", {
+  expect_equal(expand_range(c(1,1), mul = 0, add = 0.6), c(0.4, 1.6))
+  expect_equal(expand_range(c(1,1), mul = 1, add = 0.6), c(-0.6, 2.6))
+  expect_equal(expand_range(c(1,9), mul = 0, add = 2), c(-1, 11))
+})
+