Scala: tuples, arrays, maps

object Tuple { def main(args: Array[String]): Unit = { val triple1 = (100, "Scala", "Spark") println(triple1._1) println(triple1._2) println(triple1._3) //They can also be used to pass data value lists as messages between participants in concurrent programming. val triple2 = (4, 3, 2, 1) val sum = triple2._1 + triple2._2 + triple2._3 + triple2._4 println("Sum of elements: " + sum) //Iteration of tuples val triple3 = (4, 3, 2, 1) triple3.productIterator.foreach { i => println("Value = " + i) } //Tuple to string: available Tuple.toString()Method to concatenate all elements of a tuple into a string val triple4 = new Tuple3(1, "hello", Console) //Explicit use here println("Concatenated String: " + triple4.toString()) //Exchange elements: can use Tuple.swap Method exchange Tuple2 Elements in val triple5 = new Tuple2("Scala", "hello") println("Swapped Tuple: " + triple5.swap) } }

object ArrayOps { def main(args: Array[String]): Unit = { //ArrayBuffer val arraybuffer = ArrayBuffer[Int]() //Additive elements arraybuffer += 1 //use+=Add elements at the end arraybuffer += (2,3,4,5) //Add multiple elements,Can use++=Add any collection arraybuffer ++= Array(6,7,8) //Removing Elements,It can be from the head or the tail arraybuffer.trimStart(1) arraybuffer.trimEnd(3) //You can also insert or overflow elements from any location, which is not efficient arraybuffer.insert(2,11)//The first parameter is the index and the second is the insert value arraybuffer.remove(3,2)//The first parameter is index, and the second parameter is the number of removed //Sometimes you need to build a Array，But we don't know how many elements we need, we can build an array buffer arraybuffer.toArray //Traversal of array val array = Array(1, 2, 3, 4, 5) //until yes RichInt Class to return all data less than the upper limit for (i <- 0 until array.length) { println(array(i)) } //If we don't need subscripts in the loop body, we can directly access array elements for(elem <- array){ println(elem) } arraybuffer.sum arraybuffer.max arraybuffer.sorted //Multidimensional array //this Double The multidimensional array type of is Array[Array[Double]],Construct this array using ofDim Method val matrix1 = Array.ofDim[Double](3,4)//3 Row, 4 column //Access element //matrix1(row)(column) //Irregular array, each row has different length val matrix2=new Array[Array[Int]](10) for(i <- 0 until matrix2.length){ matrix2(i) = new Array[Int](i+1) } //Array conversion //yield val a = Array(2,3,5,6) val result = for(elem <- a) yield 2 * elem //If you are not satisfied, you can pass the guard val result1 = for(elem <- a if elem % 2==0) yield 2 * elem } }

object MapOps { def main(args: Array[String]): Unit = { var scores1=Map("john" -> 10,"Alice" -> 20,"Bob" -> 30) //The above code constructs an immutable mapping Map[String,Int],Its value cannot be changed,because Map The default is to call immutable The source code of the package is: val Map = immutable.Map //Variable mapping val scores2=scala.collection.mutable.Map("john" -> 10,"Alice" -> 20,"Bob" -> 30) //Empty mapping, type selection required val scores3=new scala.collection.mutable.HashMap[String ,Int] //Get the value in the map: you can get the value according to the key val johnScore=scores1("john")//Similar Java Medium scores.get("john") //Check if a value is included in the map val bobScore = if(scores1.contains("Bob")) scores1("Bob") else 0 //Shortcut writing val aliceScore = scores1.getOrElse("Alice",0) //Update the value in the map, which needs to be in the variable map scores2("john")=80 scores2 += ("Boole" -> 50,"LiLei" -> 45) //Although immutable mapping is immutable by definition, you can val newScores=scores1 + ("HanMei" -> 99) //Similarly, you need to remove a value from the immutable map to use-Unmap the key scores1 = scores1 - "Alice" //Iterative mapping: you can Scala Of for Using pattern matching in a loop //If you only need access to keys and values, you can use the keySet and values，values Method returns a Iterable，You can use this in a loop Iterable scores1.keySet //A similar Set Of("john","Alice","Bob" )Such sets for(i <- scores1.values) println(i) //Sorted map:By default, Scala Given a hash table, we need to access all keys in order. We need a tree map val scores4 = scala.collection.immutable.SortedMap("john" -> 10,"Alice" -> 20,"Bob" -> 30) //If you want to insert all keys in order val scores5 = scala.collection.mutable.LinkedHashMap("john" -> 10,"Alice" -> 20,"Bob" -> 30) } }

2 December 2019, 15:31 | Views: 2950