如何通过在Scala Spark中键入键来连接两个数据集

Question

I have two datasets and each dataset have two elements. Below are examples.

Data1: (name, animal)

('abc,def', 'monkey(1)')
('df,gh', 'zebra')
...

Data2: (name, fruit)

('a,efg', 'apple')
('abc,def', 'banana(1)')
...

Results expected: (name, animal, fruit)

('abc,def', 'monkey(1)', 'banana(1)')
... 

I want to join these two datasets by using first column 'name.' I have tried to do this for a couple of hours, but I couldn't figure out. Can anyone help me?

val sparkConf = new SparkConf().setAppName("abc").setMaster("local[2]")
val sc = new SparkContext(sparkConf)
val text1 = sc.textFile(args(0))
val text2 = sc.textFile(args(1))

val joined = text1.join(text2)

Above code is not working!

Answer 1

join is defined on RDDs of pairs, that is, RDDs of type RDD[(K,V)] . The first step needed is to transform the input data into the right type.

We first need to transform the original data of type String into pairs of (Key, Value) :

val parse:String => (String, String) = s => {
  val regex = "^\\('([^']+)',[\\W]*'([^']+)'\\)$".r
  s match {
    case regex(k,v) => (k,v)
    case _ => ("","")
  }
}

(Note that we can't use a simple split(",") expression because the key contains commas)

Then we use that function to parse the text input data:

val s1 = Seq("('abc,def', 'monkey(1)')","('df,gh', 'zebra')")
val s2 = Seq("('a,efg', 'apple')","('abc,def', 'banana(1)')")

val rdd1 = sparkContext.parallelize(s1)
val rdd2 = sparkContext.parallelize(s2)

val kvRdd1 = rdd1.map(parse)
val kvRdd2 = rdd2.map(parse)

Finally, we use the join method to join the two RDDs

val joined = kvRdd1.join(kvRdd2)

// Let's check out results

joined.collect

// res31: Array[(String, (String, String))] = Array((abc,def,(monkey(1),banana(1))))

Answer 2

You have to create pairRDDs first for your data sets then you have to apply join transformation. Your data sets are not looking accurate.

Please consider the below example.

**Dataset1**

a 1
b 2
c 3

**Dataset2**

a 8
b 4

Your code should be like below in Scala

    val pairRDD1 = sc.textFile("/path_to_yourfile/first.txt").map(line => (line.split(" ")(0),line.split(" ")(1)))

    val pairRDD2 = sc.textFile("/path_to_yourfile/second.txt").map(line => (line.split(" ")(0),line.split(" ")(1)))

    val joinRDD = pairRDD1.join(pairRDD2)

    joinRDD.collect

Here is the result from scala shell

res10: Array[(String, (String, String))] = Array((a,(1,8)), (b,(2,4)))