coord_trans() now generates a warning when a transformation results…

… in x or y values being non-finite (tidyverse#2147).

R/coord-transform.r

@@ -119,8 +119,12 @@ CoordTrans <- ggproto("CoordTrans", Coord,
     trans_x <- function(data) transform_value(self$trans$x, data, panel_params$x.range)
     trans_y <- function(data) transform_value(self$trans$y, data, panel_params$y.range)
 
-    data <- transform_position(data, trans_x, trans_y)
-    transform_position(data, squish_infinite, squish_infinite)
+    new_data <- transform_position(data, trans_x, trans_y)
+
+    warn_new_infinites(data$x, new_data$x, "x")
+    warn_new_infinites(data$y, new_data$y, "y")
+
+    transform_position(new_data, squish_infinite, squish_infinite)
   },
 
   setup_panel_params = function(self, scale_x, scale_y, params = list()) {
@@ -174,3 +178,14 @@ train_trans <- function(scale, limits, trans, name) {
   names(out) <- paste(name, names(out), sep = ".")
   out
 }
+
+# Generate warning when finite values are transformed into infinite values
+#
+# @param old_values A vector of pre-transformation values.
+# @param new_values A vector of post-transformation values.
+# @param axis Which axis the values originate from (e.g. x, y).
+warn_new_infinites <- function(old_values, new_values, axis) {
+  if (any(is.finite(old_values) & !is.finite(new_values))) {
+    warning("Transformation introduced infinite values in ", axis, "-axis", call. = FALSE)
+  }
+}

tests/testthat/test-coord-transform.R

@@ -0,0 +1,22 @@
+context("coord_trans")
+
+test_that("warnings are generated when cord_trans() results in new infinite values", {
+  p  <- ggplot(head(diamonds, 20)) +
+    geom_bar(aes(x = cut)) +
+    coord_trans(y = "log10")
+
+  p2 <- ggplot(data.frame(a = c(1, 2, 0), b = c(10, 6, 4)), aes(a, b)) +
+    geom_point() +
+    coord_trans(x = "log")
+
+  expect_warning(ggplot_gtable(ggplot_build(p)), "Transformation introduced infinite values in y-axis")
+  expect_warning(ggplot_gtable(ggplot_build(p2)), "Transformation introduced infinite values in x-axis")
+})
+
+test_that("no warnings are generated when original data has Inf values, but no new Inf values created from the transformation", {
+  p <- ggplot(data.frame(x = c(-Inf, 2, 0), y = c(Inf, 6, 4)), aes(x, y)) +
+    geom_point() +
+    coord_trans(x = 'identity')
+
+  expect_silent(benchplot(p))
+})