scala循环遍历

to

for (i <- 1 to 3) {
  println(i)
}
//相当于
val range=(1 to 3) //range: scala.collection.immutable.Range.Inclusive = Range(1, 2, 3)
range.foreach(println)

until

for (i <- 1 until 3) {
  println("i: " + i)
}
//i: 1
//i: 2

多范围

for( i <- 1 to 3; j <- 1 to 3){
    //...
}
//相当于
for( i <- 1 to 3){
  for( j <- 1 to 3){
    //...
  }
}

List

val list=List(1,2,3) //  list: List[Int] = List(1, 2, 3)
for (elem <- list) {
  println(elem)
}
// 1
// 2
// 3

条件

val list = List(1, 2, 3, 4, 5, 6);

for (i <- list if i != 3; if i < 5) {
  println("i: " + i);
}
//相当于
for (i <- list) {
  if (i != 3 && i < 5) {
    println("i: " + i);
  }
}
// i: 1
// i: 2
// i: 4

yield

返回for循环中符合条件的变量值并组成被遍历的类型

val list = List(1,2,3,4,5,6) // list: List[Int] = List(1, 2, 3, 4, 5, 6)

var retVal = for{ i <- list
                  if i != 3; if i < 5
} yield i // retVal: List[Int] = List(1, 2, 4)

for( i <- retVal){
  println( "i: " + i );
}
// i: 1
// i: 2
// i: 4