[SPARK-7435] [SPARKR] Make DataFrame.show() consistent with that of Scala and pySpark

Author: Joshi <[email protected]>
Author: Rekha Joshi <[email protected]>

Closes apache#5989 from rekhajoshm/fix/SPARK-7435 and squashes the following commits:

cfc9e02 [Joshi] Spark-7435[R]: updated patch for review comments
62becc1 [Joshi] SPARK-7435: Update to DataFrame
e3677c9 [Rekha Joshi] Merge pull request #1 from apache/master

(cherry picked from commit b94a933)
Signed-off-by: Shivaram Venkataraman <[email protected]>

Author: rekhajoshm

R/pkg/R/DataFrame.R

@@ -150,7 +150,7 @@ setMethod("isLocal",
             callJMethod(x@sdf, "isLocal")
           })
 
-#' ShowDF
+#' showDF
 #'
 #' Print the first numRows rows of a DataFrame
 #'
@@ -170,7 +170,8 @@ setMethod("isLocal",
 setMethod("showDF",
           signature(x = "DataFrame"),
           function(x, numRows = 20) {
-            callJMethod(x@sdf, "showString", numToInt(numRows))
+            s <- callJMethod(x@sdf, "showString", numToInt(numRows))
+            cat(s)
           })
 
 #' show
@@ -187,7 +188,7 @@ setMethod("showDF",
 #' sqlCtx <- sparkRSQL.init(sc)
 #' path <- "path/to/file.json"
 #' df <- jsonFile(sqlCtx, path)
-#' show(df)
+#' df
 #'}
 setMethod("show", "DataFrame",
           function(object) {

R/pkg/inst/tests/test_sparkSQL.R

@@ -653,7 +653,8 @@ test_that("toJSON() returns an RDD of the correct values", {
 
 test_that("showDF()", {
   df <- jsonFile(sqlCtx, jsonPath)
-  expect_output(showDF(df), "+----+-------+\n| age|   name|\n+----+-------+\n|null|Michael|\n|  30|   Andy|\n|  19| Justin|\n+----+-------+\n")
+  s <- capture.output(showDF(df))
+  expect_output(s , "+----+-------+\n| age|   name|\n+----+-------+\n|null|Michael|\n|  30|   Andy|\n|  19| Justin|\n+----+-------+\n")
 })
 
 test_that("isLocal()", {