Adds support of pipeRDD().

Author: hlin09

pkg/NAMESPACE

@@ -41,6 +41,7 @@ exportMethods(
               "numPartitions",
               "partitionBy",
               "persist",
+              "pipeRDD",
               "reduce",
               "reduceByKey",
               "reduceByKeyLocally",

pkg/R/RDD.R

@@ -1275,6 +1275,43 @@ setMethod("aggregateRDD",
             Reduce(combOp, partitionList, zeroValue)
           })
 
+#' Pipes elements to a forked externel process.
+#'
+#' The same as 'pipe()' in Spark.
+#'
+#' @param rdd The RDD whose elements are piped to the forked externel process.
+#' @param command The command to fork an externel process.
+#' @param env A named list to set environment variables of the externel process.
+#' @return A new RDD created by piping all elements to a forked externel process.
+#' @rdname pipeRDD
+#' @export
+#' @examples
+#'\dontrun{
+#' sc <- sparkR.init()
+#' rdd <- parallelize(sc, 1:10)
+#' collect(pipeRDD(rdd, "more")
+#' Output: c("1", "2", ..., "10")
+#'}
+setGeneric("pipeRDD", function(rdd, command, env = list()) { 
+  standardGeneric("pipeRDD") 
+})
+
+#' @rdname pipeRDD
+#' @aliases pipeRDD,RDD,character-method
+setMethod("pipeRDD",
+          signature(rdd = "RDD", command = "character"),
+          function(rdd, command, env = list()) {
+            func <- function(part) {
+              trim.trailing.func <- function(x) {
+                sub("[\r\n]*$", "", toString(x))
+              }
+              input <- unlist(lapply(part, trim.trailing.func))
+              res <- system2(command, stdout = TRUE, input = input, env = env)
+              lapply(res, trim.trailing.func)
+            }
+            lapplyPartition(rdd, func)
+          })
+
 # TODO: Consider caching the name in the RDD's environment
 #' Return an RDD's name.
 #'

pkg/inst/tests/test_rdd.R

@@ -336,6 +336,18 @@ test_that("values() on RDDs", {
   expect_equal(actual, lapply(intPairs, function(x) { x[[2]] }))
 })
 
+test_that("pipeRDD() on RDDs", {
+  actual <- collect(pipeRDD(rdd, "more"))
+  expected <- as.list(as.character(1:10))
+  expect_equal(actual, expected)
+  
+  rev.nums <- 9:0
+  rev.rdd <- parallelize(sc, rev.nums, 2L)
+  actual <- collect(pipeRDD(rev.rdd, "sort"))
+  expected <- as.list(as.character(c(5:9, 0:4)))
+  expect_equal(actual, expected)
+})
+
 test_that("join() on pairwise RDDs", {
   rdd1 <- parallelize(sc, list(list(1,1), list(2,4)))
   rdd2 <- parallelize(sc, list(list(1,2), list(1,3)))

pkg/man/pipeRDD.Rd

@@ -0,0 +1,34 @@
+% Generated by roxygen2 (4.1.0): do not edit by hand
+% Please edit documentation in R/RDD.R
+\docType{methods}
+\name{pipeRDD}
+\alias{pipeRDD}
+\alias{pipeRDD,RDD,character-method}
+\title{Pipes elements to a forked externel process.}
+\usage{
+pipeRDD(rdd, command, env = list())
+
+\S4method{pipeRDD}{RDD,character}(rdd, command, env = list())
+}
+\arguments{
+\item{rdd}{The RDD whose elements are piped to the forked externel process.}
+
+\item{command}{The command to fork an externel process.}
+
+\item{env}{A named list to set environment variables of the externel process.}
+}
+\value{
+A new RDD created by piping all elements to a forked externel process.
+}
+\description{
+The same as 'pipe()' in Spark.
+}
+\examples{
+\dontrun{
+sc <- sparkR.init()
+rdd <- parallelize(sc, 1:10)
+collect(pipeRDD(rdd, "more")
+Output: c("1", "2", ..., "10")
+}
+}
+