Spark基礎

1 讀取本地文件

./spark-shell 

scala> val textFile=sc.textFile("file:///home/hadoop/wordfile1.txt")
textFile: org.apache.spark.rdd.RDD[String] = file:///home/hadoop/wordfile1.txt MapPartitionsRDD[3] at textFile at <console>:24

scala> textFile.first()
res2: String = I love Spark

2 讀取hdfs文件

首先要啓動hdfs，而後上傳文件至hdfs，才能用下面的命令讀取。

scala> val textFile=sc.textFile("hdfs://localhost:9000/user/hadoop/input/wordfile1.txt")
textFile: org.apache.spark.rdd.RDD[String] = hdfs://localhost:9000/user/hadoop/input/wordfile1.txt MapPartitionsRDD[7] at textFile at <console>:24

scala> textFile.first()
res4: String = I love Spark

scala> val textFile=sc.textFile("input/wordfile1.txt")
textFile: org.apache.spark.rdd.RDD[String] = input/wordfile1.txt MapPartitionsRDD[9] at textFile at <console>:24

scala> textFile.first()
res5: String = I love Spark

scala> val textFile=sc.textFile("/user/hadoop/input/wordfile1.txt")
textFile: org.apache.spark.rdd.RDD[String] = /user/hadoop/input/wordfile1.txt MapPartitionsRDD[11] at textFile at <console>:24

scala> textFile.count()
res6: Long = 2

scala> textFile.first()
res8: String = I love Spark

3 詞頻統計

scala> val wordCount=textFile.flatMap(line=>line.split(" ")).map(word=>(word,1)).reduceByKey((a,b)=>(a+b))
wordCount: org.apache.spark.rdd.RDD[(String, Int)] = ShuffledRDD[14] at reduceByKey at <console>:26

scala> wordCount.collect()res9: Array[(String, Int)] = Array((Spark,1), (love,2), (I,2), (Hadoop,1))