Github user felixcheung commented on a diff in the pull request:
https://github.com/apache/spark/pull/17851#discussion_r114724979
--- Diff: R/pkg/R/DataFrame.R ---
@@ -3715,3 +3715,34 @@ setMethod("rollup",
sgd <- callJMethod(x@sdf, "rollup", jcol)
groupedData(sgd)
})
+
+#' hint
+#'
+#' Specifies execution plan hint on the current SparkDataFrame.
+#'
+#' @param x a SparkDataFrame.
+#' @param name a name of the hint.
+#' @param ... additional argument(s) passed to the method.
+#'
+#' @return A SparkDataFrame.
+#' @family SparkDataFrame functions
+#' @aliases hint,SparkDataFrame,character-method
+#' @rdname hint
+#' @name hint
+#' @export
+#' @examples
+#' \dontrun{
+#' df <- createDataFrame(mtcars)
+#' avg_mpg <- mean(groupBy(createDataFrame(mtcars), "cyl"), "mpg")
--- End diff --
right - I think the example makes sense now but it might not be very
obvious - for example,
```
createDataFrame(mtcars)
createDataFrame(mtcars)
```
vs
```
df <- createDataFrame(mtcars)
df
```
is not very subtle unless you know what Spark is doing differently here.
This is why I suggested pointing out the need to have distinct "copies" of data
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