Overview of key-value pairs"Key-value pair" is a relatively common RDD element type, which is often used in grouping and aggregation operations. "Pair RDD" (Pair RDD) is often used in Spark operations to complete aggregation calculations. The data type stored in the ordinary RDD is Int, String, etc., while the data type stored in the "key-value pair RDD" is "key-value pair".scala> val pairRDD = sc.parallelize(List("this is demo","how do you do","fine,thank you")) pairRDD: org.apache.spark.rdd

statementvar list = List(1,2,3,4) println(list)Empty listvar foo = List() println(foo) var bar = Nil println(bar)::The :: (two colons) operator is right-associative. If you want to build a list List(1,2,3,4), you can actually use the following method, Nil means an empty list.scala> 1::2::3::4::Nil res6: List[Int] = List(1, 2, 3, 4)A list has the concept of a head and a tail. It headreturns the first element of the list and tailreturns a list, except 第一元素之外的其他元素that the head is an element, and

The action operation is where the calculation is actually triggered. When the Spark program executes the action operation, the real calculation is performed, the data is loaded from the file, and the conversion operation is completed again and again, and finally, the action operation is completed and the result is obtained.operatingDescriptioncount()Returns the number of elements in the data setcollect()Return all elements in the data set in the form of an arrayfirst()Returns the first element i

matchWhen you need to select from multiple branches, similar to the switch statement in Java, you don't need to use break to stop code execution.Variable match { case value1 => code 1 case value2 => code 2 ... case _ => code N }eg:import scala.util.Random object MatchApp extends App{ val numbers = Array("one","two","three") val number = numbers(Random.nextInt(numbers.length)) number match { case "one" => println("1") case "two" => println("2") case _ => println("3") } }image.pn