[SPARK-6799] [SPARKR] Remove SparkR RDD examples, add dataframe examples

This PR also makes some of the DataFrame to RDD methods private as the RDD class is private in 1.4

cc rxin pwendell

Author: Shivaram Venkataraman <shivaram@cs.berkeley.edu>

Closes apache#5949 from shivaram/sparkr-examples and squashes the following commits:

6c42fdc [Shivaram Venkataraman] Remove SparkR RDD examples, add dataframe examples

R/pkg/NAMESPACE

@@ -45,8 +45,6 @@ exportMethods("cache",
               "showDF",
               "sortDF",
               "take",
-              "toJSON",
-              "toRDD",
               "unionAll",
               "unpersist",
               "where",
@@ -95,14 +93,12 @@ export("cacheTable",
        "createExternalTable",
        "dropTempTable",
        "jsonFile",
-       "jsonRDD",
        "loadDF",
        "parquetFile",
        "sql",
        "table",
        "tableNames",
        "tables",
-       "toDF",
        "uncacheTable")
 
 export("sparkRSQL.init",

R/pkg/R/DataFrame.R

@@ -272,7 +272,7 @@ setMethod("names",
 setMethod("registerTempTable",
           signature(x = "DataFrame", tableName = "character"),
           function(x, tableName) {
-              callJMethod(x@sdf, "registerTempTable", tableName)
+              invisible(callJMethod(x@sdf, "registerTempTable", tableName))
           })
 
 #' insertInto

examples/src/main/r/dataframe.R

@@ -0,0 +1,54 @@
+#
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.
+# The ASF licenses this file to You under the Apache License, Version 2.0
+# (the "License"); you may not use this file except in compliance with
+# the License.  You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+library(SparkR)
+
+# Initialize SparkContext and SQLContext
+sc <- sparkR.init(appName="SparkR-DataFrame-example")
+sqlContext <- sparkRSQL.init(sc)
+
+# Create a simple local data.frame
+localDF <- data.frame(name=c("John", "Smith", "Sarah"), age=c(19, 23, 18))
+
+# Convert local data frame to a SparkR DataFrame
+df <- createDataFrame(sqlContext, localDF)
+
+# Print its schema
+printSchema(df)
+# root
+#  |-- name: string (nullable = true)
+#  |-- age: double (nullable = true)
+
+# Create a DataFrame from a JSON file
+path <- file.path(Sys.getenv("SPARK_HOME"), "examples/src/main/resources/people.json")
+peopleDF <- jsonFile(sqlContext, path)
+printSchema(peopleDF)
+
+# Register this DataFrame as a table.
+registerTempTable(peopleDF, "people")
+
+# SQL statements can be run by using the sql methods provided by sqlContext
+teenagers <- sql(sqlContext, "SELECT name FROM people WHERE age >= 13 AND age <= 19")
+
+# Call collect to get a local data.frame
+teenagersLocalDF <- collect(teenagers)
+
+# Print the teenagers in our dataset 
+print(teenagersLocalDF)
+
+# Stop the SparkContext now
+sparkR.stop()