Improve facet error messages in animint2dir

DESCRIPTION

@@ -1,6 +1,6 @@
 Package: animint2
 Title: Animated Interactive Grammar of Graphics
-Version: 2026.9.5
+Version: 2026.9.28
 URL: https://animint.github.io/animint2
 BugReports: https://github.com/animint/animint2/issues
 Authors@R: c(

NEWS.md

@@ -1,3 +1,7 @@
+# Changes in version 2026.9.28 (PR#285)
+
+- Clearer facet error messages when a facet variable is missing from the data, or when `facet_wrap(. ~ var)` uses invalid notation (issue #168).
+
 # Changes in version 2026.9.5
 
 - geom_text() renders with .text(), instead of setMultilineText(), fixing interactive updates.

R/facet-layout.r

@@ -48,6 +48,20 @@ layout_wrap <- function(data, vars = NULL, nrow = NULL, ncol = NULL,
   vars <- as.quoted(vars)
   if (length(vars) == 0) return(layout_null())
 
+  # Notation error only when real vars exist; otherwise layout_base reports missing columns.
+  if ("." %in% names(vars)) {
+    real_vars <- names(vars)[names(vars) != "."]
+    all_data_vars <- unique(unlist(lapply(data, names)))
+    missing_vars <- setdiff(real_vars, all_data_vars)
+    if (length(missing_vars) == 0) {
+      stop(sprintf(
+        "Invalid facet_wrap formula (. ~ var). Use facet_wrap(~%s) or facet_wrap(\"%s\")",
+        paste(real_vars, collapse = " + "),
+        paste(real_vars, collapse = "\", \"")
+      ), call. = FALSE)
+    }
+  }
+
   base <- plyr::unrowname(layout_base(data, vars, drop = drop))
 
   id <- plyr::id(base, drop = TRUE)
@@ -93,8 +107,22 @@ layout_base <- function(data, vars = NULL, drop = TRUE) {
 
   # Form the base data frame which contains all combinations of facetting
   # variables that appear in the data
-  has_all <- unlist(plyr::llply(values, length)) == length(vars)
+  has_all <- unlist(lapply(values, length)) == length(vars)
   if (!any(has_all)) {
+    all_data_vars <- unique(unlist(lapply(data, names)))
+    missing_vars <- setdiff(names(vars)[names(vars) != "."], all_data_vars)
+    if (length(missing_vars) > 0) {
+      stop(sprintf(
+        "Facet variable%s not found in data: %s\nAvailable columns: %s",
+        if (length(missing_vars) > 1) "s" else "",
+        paste(missing_vars, collapse = ", "),
+        paste(all_data_vars, collapse = ", ")
+      ))
+    }
+    # Reached when all facet variables exist somewhere in the data, but no
+    # single layer has all of them together. For example, facet_grid(X ~ Y)
+    # where layer 1 only has column X and layer 2 only has column Y — neither
+    # layer alone satisfies all facetting variables, so has_all is FALSE for every layer.
     stop("At least one layer must contain all variables used for facetting")
   }
 

tests/testthat/test-compiler-ghpages.R

@@ -51,6 +51,28 @@ reset_test_repo <- function(){
   gh::gh("POST /orgs/animint-test/repos", name = test_repo_name)
   Sys.sleep(3)
 }
+clone_test_repo <- function(github_url, new_clone){
+  max_attempts <- 5
+  wait_seconds <- 3
+  last_error <- NULL
+  for (attempt in seq_len(max_attempts)) {
+    result <- tryCatch({
+      clone <- gert::git_clone(github_url, new_clone)
+      last_error <- NULL
+      clone
+    }, error = function(err){
+      last_error <<- err
+      NULL
+    })
+    if (is.null(last_error)) return(result)
+    if (!grepl("status code: 404", conditionMessage(last_error), fixed = TRUE)) {
+      stop(last_error)
+    }
+    unlink(new_clone, recursive = TRUE, force = TRUE)
+    if (attempt < max_attempts) Sys.sleep(wait_seconds)
+  }
+  stop(last_error)
+}
 test_that("animint2pages(chromote_sleep_seconds=3) creates Capture.PNG", {
   reset_test_repo()
   ## first run of animint2pages creates new data viz.
@@ -96,7 +118,7 @@ test_that("animint2pages(chromote_sleep_seconds=NULL) does not create Capture.PN
   ## clone and add Capture.PNG
   new_clone <- tempfile()
   github_url <- paste0("https://github.com/", result_list$owner_repo, ".git")
-  gert::git_clone(github_url, new_clone)
+  clone_test_repo(github_url, new_clone)
   branch_name <- gert::git_branch(new_clone)
   expect_identical(branch_name, "gh-pages", info=paste(branch_name, "should be gh-pages"))
   cat("FOO", file=file.path(new_clone, "Capture.PNG"))

tests/testthat/test-renderer-facet-error-messages.R

@@ -0,0 +1,79 @@
+acontext("Facet error messages")
+missing_var_error <- paste(
+  "Facet variable not found in data: NonExistentColumn",
+  "Available columns: Sepal.Length, Sepal.Width, Petal.Length, Petal.Width, Species",
+  sep = "\n"
+)
+missing_var_string_error <- paste(
+  "Facet variable not found in data: MissingVar",
+  "Available columns: Sepal.Length, Sepal.Width, Petal.Length, Petal.Width, Species",
+  sep = "\n"
+)
+bad_notation_error <- "Invalid facet_wrap formula (. ~ var). Use facet_wrap(~Species) or facet_wrap(\"Species\")"
+test_that("facet_wrap string missing variable gives clear error", {
+  viz <- list(
+    scatter = ggplot() +
+      facet_wrap("MissingVar") +
+      geom_point(aes(Sepal.Length, Petal.Length), data = iris)
+  )
+  expect_error({
+    animint2dir(viz)
+  }, missing_var_string_error, fixed = TRUE)
+})
+test_that("facet_wrap formula with missing variable gives clear error", {
+  viz <- list(
+    scatter = ggplot() +
+      facet_wrap(. ~ NonExistentColumn) +
+      geom_point(aes(Sepal.Length, Petal.Length), data = iris)
+  )
+  expect_error({
+    animint2dir(viz)
+  }, missing_var_error, fixed = TRUE)
+})
+test_that("facet_wrap bad notation when variable exists gives clear error", {
+  viz <- list(
+    scatter = ggplot() +
+      facet_wrap(. ~ Species) +
+      geom_point(aes(Sepal.Length, Petal.Length), data = iris)
+  )
+  expect_error({
+    animint2dir(viz)
+  }, bad_notation_error, fixed = TRUE)
+})
+test_that("facet_grid missing variable gives clear error", {
+  viz <- list(
+    scatter = ggplot() +
+      facet_grid(. ~ MissingVar) +
+      geom_point(aes(Sepal.Length, Petal.Length), data = iris)
+  )
+  expect_error({
+    animint2dir(viz)
+  }, missing_var_string_error, fixed = TRUE)
+})
+test_that("facet_wrap tilde notation works", {
+  viz <- list(
+    scatter = ggplot() +
+      facet_wrap(~Species) +
+      geom_point(aes(Sepal.Length, Petal.Length), data = iris)
+  )
+  info <- animint2dir(viz, open.browser = FALSE)
+  expect_true(file.exists(file.path(info$out.dir, "index.html")))
+})
+test_that("facet_wrap string notation works", {
+  viz <- list(
+    scatter = ggplot() +
+      facet_wrap("Species") +
+      geom_point(aes(Sepal.Length, Petal.Length), data = iris)
+  )
+  info <- animint2dir(viz, open.browser = FALSE)
+  expect_true(file.exists(file.path(info$out.dir, "index.html")))
+})
+test_that("facet_grid formula notation works", {
+  viz <- list(
+    scatter = ggplot() +
+      facet_grid(. ~ Species) +
+      geom_point(aes(Sepal.Length, Petal.Length), data = iris)
+  )
+  info <- animint2dir(viz, open.browser = FALSE)
+  expect_true(file.exists(file.path(info$out.dir, "index.html")))
+})

tests/testthat/test-renderer3-knit-print.R

@@ -181,6 +181,7 @@ click_center <- function(id){
     ## https://github.com/rstudio/chromote/issues/32
     do.call(remDr$Input$dispatchMouseEvent, L)
   }
+  Sys.sleep(1)
 }
 
 djs.init.list <- driverjs_get(html)