Issue668

NEWS.md

@@ -13,6 +13,11 @@ where the formatting is also better._
 - `type_hexbin()` (equivalently, `type = "hexbin"`) for hexagonal bin plots, a
   2D analogue of a histogram. (#667 @grantmcdermott)
 
+### Bug fixes
+
+- Fixed bug where single-valued discrete axes would trigger invalid `par(usr)`
+  values when combined with free facets. (#668 @grantmcdermott)
+
 ## v0.7.0
 
 **tinyplot** v0.7.0 is a big release with many new features, including major

R/facet.R

@@ -368,6 +368,11 @@ draw_facet_window = function(
         # extendrange() returns an ascending pair, so reverse afterwards
         xext = extendrange(sort(xlim), f = 0.04)
         yext = extendrange(sort(ylim), f = 0.04)
+        # A facet with a single distinct x (or y) value yields a zero-width
+        # extent, which par(usr=) rejects. Mirror base plot.window() and pad
+        # a degenerate range symmetrically so the facet still draws. (#668)
+        if (diff(xext) == 0) xext = xext + c(-1, 1) * (if (xext[1L] == 0) 1 else 0.04 * abs(xext[1L]))
+        if (diff(yext) == 0) yext = yext + c(-1, 1) * (if (yext[1L] == 0) 1 else 0.04 * abs(yext[1L]))
         # base axTicks() misbehaves on a reversed usr (it collapses to a single
         # tick), so precompute ticks from the ascending extent and pass them as
         # an explicit `at` below; placement against the reversed usr is fine.

inst/tinytest/test-facet.R

@@ -556,6 +556,22 @@ f = function() {
 }
 expect_snapshot_plot(f, label = "facet_free_yscale")
 
+# Free facets where a facet has a single distinct (discrete) axis value, which
+# collapses the free-scale range to zero width (issue #668)
+f = function() {
+  dat = data.frame(
+    x = c("a", "b", "b"),
+    y = c(1, 2, 3),
+    g = c("A", "B", "B")
+  )
+  tinyplot(
+    y ~ x, data = dat,
+    facet = ~g, facet.args = list(free = TRUE),
+    main = "Free facets: single-value facet"
+  )
+}
+expect_snapshot_plot(f, label = "facet_free_single_value")
+
 #
 # restore original par settings
 #