Github user gatorsmile commented on a diff in the pull request:
https://github.com/apache/spark/pull/12836#discussion_r61708838
--- Diff: R/pkg/R/DataFrame.R ---
@@ -1187,6 +1187,65 @@ setMethod("dapply",
dataFrame(sdf)
})
+#' gapply
+#'
+#' Apply a function to each group of a DataFrame.
+#'
+#' @param x A SparkDataFrame
+#' @param func A function to be applied to each group partition specified
by grouping
+#' column of the SparkDataFrame.
+#' The output of func is a data.frame.
+#' @param schema The schema of the resulting DataFrame after the function
is applied.
+#' It must match the output of func.
+#' @family SparkDataFrame functions
+#' @rdname gapply
+#' @name gapply
+#' @export
+#' @examples
+#' \dontrun{
+#' df <- createDataFrame (sqlContext, iris)
+#' gdf <- gapply(df, function(x) { x }, schema(df), "Petal_Width")
+#' collect(gdf)
+#'
+#' Compute the square of the first columns and output it
+#'
+#' df <- createDataFrame (
+#' sqlContext,
+#' list(list(1L, 1, "1", 0.1), list(1L, 2, "2", 0.2), list(3L, 3, "3",
0.3)),
+#' c("a", "b", "c", "d"))
+#'
+#' schema <- structType(structField("result", "integer"))
+#' df1 <- gapply(
+#' df,
+#' function(x) {
+#' y <- x[1] * x[1]
+#' },
+#' schema, "a")
+#' collect(df1)
+#'
+#' result
+#' ------
+#' 1
+#' 1
+#' 9
--- End diff --
This example is not good for `flatMapGroups`.
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