[SPARK-6856] [R] Make RDD information more useful in SparkR

Author: Jeff Harrison <jeffrharrison@gmail.com>

Closes #5667 from His-name-is-Joof/joofspark and squashes the following commits:

f8814a6 [Jeff Harrison] newline added after RDD show() output
4d9d972 [Jeff Harrison] Merge branch 'master' into joofspark
9d2295e [Jeff Harrison] parallelize with 1:10
878b830 [Jeff Harrison] Merge branch 'master' into joofspark
c8c0b80 [Jeff Harrison] add test for RDD function show()
123be65 [Jeff Harrison] SPARK-6856

R/pkg/R/RDD.R

@@ -66,6 +66,11 @@ setMethod("initialize", "RDD", function(.Object, jrdd, serializedMode,
   .Object
 })
 
+setMethod("show", "RDD",
+          function(.Object) {
+              cat(paste(callJMethod(.Object@jrdd, "toString"), "\n", sep=""))
+          })
+
 setMethod("initialize", "PipelinedRDD", function(.Object, prev, func, jrdd_val) {
   .Object@env <- new.env()
   .Object@env$isCached <- FALSE

R/pkg/inst/tests/test_rdd.R

@@ -759,6 +759,11 @@ test_that("collectAsMap() on a pairwise RDD", {
   expect_equal(vals, list(`1` = "a", `2` = "b"))
 })
 
+test_that("show()", {
+  rdd <- parallelize(sc, list(1:10))    
+  expect_output(show(rdd), "ParallelCollectionRDD\\[\\d+\\] at parallelize at RRDD\\.scala:\\d+")
+})
+
 test_that("sampleByKey() on pairwise RDDs", {
   rdd <- parallelize(sc, 1:2000)
   pairsRDD <- lapply(rdd, function(x) { if (x %% 2 == 0) list("a", x) else list("b", x) })