scala-笔记1
一直想写些技术性的笔记，以便自己加深印象以及方便其他人阅读。奈于对自己的文字功底实在不敢恭维，甚至一直舍不得花时间投入这种输出性的写作事项，一直拖到现在。希望自己能坚持下去!
```python
import tensorflow as tfprint(tf.version)
```
`
val a = List(1,2,3)
`
1:两个filter函数合并
```
defdirectedMoreThanOneFilm(numberOfFilms: Int):Seq[String] =
directors.filter(_.films.size >1).map(_.lastName)defbornBefore(year:
Int):Seq[String] = directors.filter(_.yearOfBirth >
year).map(_.lastName)
```
```scala
def and[A](f: A => Boolean, g: A => Boolean): A => Boolean = a => f(a) && g(a)
```
通过上述函数声明，我们可以将其上的两个filter函数进行合并如下：
```scala
defdirectedMoreThanOneFilm:Director=>Boolean= _.films.size >1defbornBefore(year:Int):Director=>Boolean= _.yearOfBirth > yeardefresult=directors.filter(and(directedMoreThanOneFilm, bornBefore(2018))).map(_.lastName)
```
2:将序列类型中的对象分组
```scala
case class Person(val age:Int, val name:String) {
override def toString = {
"P = " + age.toString +" / " + name +"; "
}
}
object Person {
def main(args:Array[String]):Unit = {
val persons:Seq[Person] =Seq(Person(25, "a"), Person(35, "b"), Person(27, "c"))
val m = mutable.Map[Int, Seq[Person]]()
val result =persons.map { person =>
val ageGroup = person.age /10
ageGroup -> person
}
//print each element in map method1
// result.foreach { case (bracket, person) =>
// m(bracket) = m.getOrElse(bracket, Seq[Person]()) :+ person
// }
m.foreach(println)//Having a mutable datastructure outside a function is generally frowned upon.
//method2
val resultMap:Map[Int, Seq[Person]] =result.foldLeft(mutable.Map[Int, Seq[Person]]()) {case (map, (ageGroup, person)) =>
val result2 =m.getOrElse(ageGroup, Seq[Person]()) :+person
m(ageGroup) =result2
map(ageGroup) =result2
map
}.toMap
resultMap.foreach(println)// by foldLeft
//method3
val mapGourpBy:Map[Int, Seq[Person]] =persons.groupBy(person => math.floor(person.age /10).toInt)
mapGourpBy.foreach(println)//by GroupBy
}
}
````
3:集合自动转换为函数
```scala
val myMap: Map[String, Int] = Map(
"one" -> 1,
"two" -> 2,
"three" -> 3,
"four" -> 4,
"five" -> 5,
)
val mySet = Set("one", "two", "three")
println(myMap.filterKeys(mySet)) // Why `Set[String]` could be treated as `[String] => Bool`
Set extends Function1
and it's apply is containment
remember lists do that too
@ (0 to 5).map(('a' to 'z').toList)
res9: collection.immutable.IndexedSeq[Char] = Vector('a', 'b', 'c', 'd', 'e', 'f')
```
