1. => (anonymous function)
=> Anonymous function. In Spark, a function is also an object that can be assigned to a variable.
Spark's anonymous function definition format:
(parameter list) => {function body}
Therefore, the role of => is to create an anonymous function instance.
For example: (x:Int) => x +1, which is equivalent to the following Java method:
public int function(int x) {
return x+1;
}
example:
class Symbol {
var add = (x: Int) => x + 1
}
object test2 {
def main (args: Array[String] ): Unit = {
var symbol = new Symbol
printf(""+ symbol.add.toString())
}
}
2. <- (Set traversal)
Loop traversal, examples are as follows:
var list = Array(1,2,3,4)
for (aa <- list) {
printf(aa+" ")
}
The above code is similar to the Java code:
int[] list = {
1,2,3,4};
for(int aa : list) {
System.out.print(aa+" ");
}
3.++= (string splicing)
var s:String = "a"
s+="b"
println(s)
s++="c"
println(s)
4. ::: Three colon operators and :: two colon operators
- ::: The three colon operators represent the concatenation operation of List. (Similar to list1.addAll(list2) in Java)
- :: The two colon operators represent the concatenation operation between ordinary elements and list. (Similar to the list1.add(A) operation in Java)
例子:
val one = List(1,2,3)
val two = List(4,5,6)
val three = one ::: two
println(three.toString())
val four = 7 :: three
println(four.toString())
5. -> Construct tuple and _N visit the Nth element of tuple
1. The meaning of tuples in scala:
- Tuple is a list of different types of value aggregation threads
- By enclosing multiple values in parentheses, it means a tuple
2. The difference between tuple and array in scala: the data types of the elements in the array must be the same, but the data types of the tuples can be different.
例子:
val first = (1,2,3) // 定义三元元组
val one = 1
val two = 2
val three = one -> two
println(three) // 构造二元元组
println(three._2) // 访问二元元组中第二个值
6. Usage of _ (underscore)
- Wildcard
_ can play a wildcard similar to *:
import org.apache.spark.SparkContext._
- Refers to each element in the collection
例如 遍历集合筛选列表中大于某个值的元素:
val lst = List(1,2,3,4,5)
val lstFilter = lst.filter(_ > 3)
- Get the element value of the specified subscript in the tuple
val ss = (1,"22","333")
println(ss._1)
- Use pattern matching to get the members of the tuple
val m = Map(1 -> 2,2 -> 4)
for ((k,_) <- m) println(k) //如果不需要所有部件， 则在不需要的部件使用_； 本例只取key,因此在value处用_
- Member variables instead of local variables add default values
var s:Int=_
def main(args: Array[String]): Unit = {
println(s)
}
6. +=
Add elements to the variable array
val arrBuf1 = new ArrayBuffer[Int]()
arrBuf1+= 11 // 添加一个元素
println(arrBuf1)
7. -=
Remove the corresponding value from the variable array of map
val arrBuf1 = new ArrayBuffer[Int]()
arrBuf1+= 11 // 添加一个元素
arrBuf1+= 12 // 添加一个元素
arrBuf1-= 12 // 删除一个元素
println(arrBuf1)
var map = Map(1 -> 1,2 -> 2,3 ->3 ) //key -> value
map-=1
println(map)