Scala Iterable#map与Iterable#flatMap [英] scala Iterable#map vs. Iterable#flatMap

问题描述

Iterable的map和flatMap函数之间有什么区别?

What is the difference between the map and flatMap functions of Iterable?

推荐答案

以下是一个很好的解释:

Here is a pretty good explanation:

http://www. codecommit.com/blog/scala/scala-collections-for-the-easily-bored-part-2

以列表为例:

地图的签名是:

map [B](f : (A) => B) : List[B]

和flatMap是

flatMap [B](f : (A) => Iterable[B]) : List[B]

因此，flatMap采用类型[A]并返回可迭代类型[B]，地图采用类型[A]并返回类型[B]

So flatMap takes a type [A] and returns an iterable type [B] and map takes a type [A] and returns a type [B]

这还将使您了解平面图将拉平"列表.

This will also give you an idea that flatmap will "flatten" lists.

val l  = List(List(1,2,3), List(2,3,4))

println(l.map(_.toString)) // changes type from list to string
// prints List(List(1, 2, 3), List(2, 3, 4))

println(l.flatMap(x => x)) // "changes" type list to iterable
// prints List(1, 2, 3, 2, 3, 4)

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