Github user sun-rui commented on a diff in the pull request:
https://github.com/apache/spark/pull/9023#discussion_r41704114
--- Diff: R/pkg/R/stats.R ---
@@ -100,3 +100,36 @@ setMethod("corr",
statFunctions <- callJMethod(x@sdf, "stat")
callJMethod(statFunctions, "corr", col1, col2, method)
})
+
+
+#' sampleBy
+#'
+#' Returns a stratified sample without replacement based on the fraction
given on each stratum.
+#'
+#' @param x A SparkSQL DataFrame
+#' @param col column that defines strata
+#' @param fractions A named list giving sampling fraction for each
stratum. If a stratum is
+#' not specified, we treat its fraction as zero.
+#' @param seed random seed
+#' @return A new DataFrame that represents the stratified sample
+#'
+#' @rdname statfunctions
+#' @name sampleBy
+#' @export
+#' @examples
+#'\dontrun{
+#' df <- jsonFile(sqlContext, "/path/to/file.json")
+#' sample <- sampleBy(df, "key", fractions, 36)
+#' }
+setMethod("sampleBy",
+ signature(x = "DataFrame", col = "character",
+ fractions = "list", seed = "numeric"),
+ function(x, col, fractions, seed) {
+ fractionsEnv <- convertNamedListToEnv(fractions)
--- End diff --
the signature prevents the required parameters from being missing.
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