[GitHub] [arrow] dragosmg commented on a change in pull request #12179: ARROW-14609 [R] left_join by argument error message mismatch

[GitBox <gi...@apache.org>]

dragosmg commented on a change in pull request #12179:
URL: https://github.com/apache/arrow/pull/12179#discussion_r787149579



##########
File path: r/R/dplyr-join.R
##########
@@ -117,10 +117,33 @@ handle_join_by <- function(by, x, y) {
   if (is.null(names(by))) {
     by <- set_names(by)
   }
-  # TODO: nicer messages?
-  stopifnot(
-    all(names(by) %in% names(x)),
-    all(by %in% names(y))
-  )
+
+  missing_x_cols <- setdiff(names(by), names(x))
+  if (length(missing_x_cols) > 0) {
+    message <- paste(
+      "Join",
+      ngettext(length(missing_x_cols), "column", "columns"),
+      "must be present in data."
+    )
+    message_x <- paste(
+      oxford_paste(missing_x_cols, quote_symbol = "`"),
+      "not present in x."
+      )
+    abort(c(message, x = message_x))
+  }
+
+  missing_y_cols <- setdiff(by, names(y))
+  if (length(missing_y_cols) > 0) {
+    message <- paste(
+      "Join",
+      ngettext(length(missing_y_cols), "column", "columns"),
+      "must be present in data."
+    )
+    message_y <- paste(
+      oxford_paste(missing_y_cols, quote_symbol = "`"),
+      "not present in y."
+    )
+    abort(c(message, x = message_y))
+  }

Review comment:
       I had a similar thought and I have a hunch this might be the reason for {dplyr} keeping things simpler / a bit more ambiguous. I will look into it. 




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