随着spark(1.4) 的新版本发布，似乎有一个不错的前端接口可以spark从R名为sparkR. 在R for spark 的文档页面上，有一个命令可以将json文件作为 RDD 对象读取
people <- read.df(sqlContext, "./examples/src/main/resources/people.json", "json")
我正在尝试从.csv文件中读取数据，就像在这个革命性的博客上描述的那样
# Download the nyc flights dataset as a CSV from https://s3-us-west-2.amazonaws.com/sparkr-data/nycflights13.csv
# Launch SparkR using
# ./bin/sparkR --packages com.databricks:spark-csv_2.10:1.0.3
# The SparkSQL context should already be created for you as sqlContext
sqlContext
# Java ref type org.apache.spark.sql.SQLContext id 1
# Load the flights CSV file using `read.df`. Note that we use the CSV reader Spark package here.
flights <- read.df(sqlContext, "./nycflights13.csv", "com.databricks.spark.csv", header="true")
注释说我需要一个 spark-csv 包来启用此操作。所以我用这个命令从这个github repo下载了这个包：
$ bin/spark-shell --packages com.databricks:spark-csv_2.10:1.0.3
但是后来我在尝试读取.csv文件时遇到了这样的错误。
> flights <- read.df(sqlContext, "./nycflights13.csv", "com.databricks.spark.csv", header="true")
15/07/03 12:52:41 ERROR RBackendHandler: load on 1 failed
java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.apache.spark.api.r.RBackendHandler.handleMethodCall(RBackendHandler.scala:127)
at org.apache.spark.api.r.RBackendHandler.channelRead0(RBackendHandler.scala:74)
at org.apache.spark.api.r.RBackendHandler.channelRead0(RBackendHandler.scala:36)
at io.netty.channel.SimpleChannelInboundHandler.channelRead(SimpleChannelInboundHandler.java:105)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:333)
at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:319)
at io.netty.handler.codec.MessageToMessageDecoder.channelRead(MessageToMessageDecoder.java:103)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:333)
at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:319)
at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:163)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:333)
at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:319)
at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:787)
at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:130)
at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:511)
at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:468)
at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:382)
at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:354)
at io.netty.util.concurrent.SingleThreadEventExecutor$2.run(SingleThreadEventExecutor.java:116)
at io.netty.util.concurrent.DefaultThreadFactory$DefaultRunnableDecorator.run(DefaultThreadFactory.java:137)
at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.RuntimeException: Failed to load class for data source: com.databricks.spark.csv
at scala.sys.package$.error(package.scala:27)
at org.apache.spark.sql.sources.ResolvedDataSource$.lookupDataSource(ddl.scala:216)
at org.apache.spark.sql.sources.ResolvedDataSource$.apply(ddl.scala:229)
at org.apache.spark.sql.DataFrameReader.load(DataFrameReader.scala:114)
at org.apache.spark.sql.SQLContext.load(SQLContext.scala:1230)
... 25 more
Error: returnStatus == 0 is not TRUE
关于这个错误意味着什么以及如何解决这个问题的任何想法？
当然，我可以尝试以.csv标准方式阅读，例如：
read.table("data.csv") -> flights
然后我可以将 Rdata.frame转换为spark' ，DataFrame如下所示：
flightsDF <- createDataFrame(sqlContext, flights)
但这不是我喜欢的方式，而且真的很耗时。