MichaelChirico commented on a change in pull request #28350:
URL: https://github.com/apache/spark/pull/28350#discussion_r415364659
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File path: R/pkg/R/DataFrame.R
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@@ -1669,29 +1667,43 @@ setMethod("dapplyCollect",
#' @aliases gapply,SparkDataFrame-method
#' @rdname gapply
#' @name gapply
+#' @details
+#' \code{func} is a function of two arguments. The first, usually named
\code{key}
+#' (though this is not enforced) corresponds to the grouping key, will be a
\code{list}
+#' of \code{length(cols)} length-one objects corresponding to the grouping
columns' values
+#' for the current group.
+#'
+#' The second, herein \code{x}, will be a local \code{\link{data.frame}} with
the
+#' columns of the input not in \code{cols} for the rows corresponding to
\code{key}.
+#'
+#' The output of \code{func} must be a \code{data.frame} matching
\code{schema} --
+#' in particular this means the names of the output \code{data.frame} are
irrelevant
+#'
#' @seealso \link{gapplyCollect}
#' @examples
#'
#' \dontrun{
-#' Computes the arithmetic mean of the second column by grouping
-#' on the first and third columns. Output the grouping values and the average.
+#' # Computes the arithmetic mean of the second column by grouping
Review comment:
Even though this code in `\dontrun{}` won't be evaluated by CRAN
machines, still end users might want to copy-paste the code directly & expect
it to be valid R code (this is the point of the `run.dontrun` argument for
`example()`).
So I added the comment hash here in addition to the change describing `func`
detailed above.
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