add inverse hyperbolic sin transform (#360)

NAMESPACE

@@ -37,6 +37,7 @@ export(abs_area)
 export(alpha)
 export(area_pal)
 export(as.trans)
+export(asinh_trans)
 export(asn_trans)
 export(atanh_trans)
 export(boxcox_trans)

NEWS.md

@@ -20,6 +20,9 @@
   `breaks_timespan()` adds functionality for finding pleasant breakpoints across
   the various bases in time units, while `timespan_trans()` wraps it all 
   together and provides an alternative to `hms_trans()` (#212)
+* Add an inverse (area) hyperbolic sine transformation `asinh_trans()`, which
+  provides a logarithm-like transformation of a space, but which accommodates
+  negative values (#297)
 
 # scales 1.2.1
 

R/trans-numeric.R

@@ -21,7 +21,20 @@ asn_trans <- function() {
 #' @examples
 #' plot(atanh_trans(), xlim = c(-1, 1))
 atanh_trans <- function() {
-  trans_new("atanh", "atanh", "tanh")
+  trans_new("atanh", "atanh", "tanh", domain = c(-1, 1))
+}
+
+#' Inverse Hyperbolic Sine transformation
+#'
+#' @export
+#' @examples
+#' plot(asinh_trans(), xlim = c(-1e2, 1e2))
+asinh_trans <- function() {
+  trans_new(
+    "asinh",
+    transform = asinh,
+    inverse = sinh
+  )
 }
 
 #' Box-Cox & modulus transformations

tests/testthat/test-trans-numeric.R

@@ -116,3 +116,8 @@ test_that("Yeo-Johnson transform works", {
   expect_equal(yj_trans(lambdas[2])$transform(x[[2]]), expected_data[[2]])
   expect_equal(yj_trans(lambdas[3])$transform(x[[3]]), expected_data[[3]])
 })
+
+test_that("probability transforms have domain (0,1)", {
+  expect_equal(logit_trans()$domain, c(0, 1))
+  expect_equal(probit_trans()$domain, c(0, 1))
+})