map {}和map（）有什么区别

Question

从此链接显示一些Scala示例：http :
//spark.apache.org/docs/latest/mllib-collaborative-filtering.html

map{}和之间有什么区别map()？

val ratings = data.map(_.split(',') match { case Array(user, item, rate) =>
  Rating(user.toInt, item.toInt, rate.toDouble)
})

val usersProducts = ratings.map { case Rating(user, product, rate) =>
  (user, product)
}

Answer 1

map是一种接受函数作为参数的方法。因此，通常调用map就像调用方法map（aFunction）一样。但是，Scala在语法上提供了很多灵活性/速记方式：

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

//An ordinary method call. The braces just evaluate to an anonymous function
val a = list.map({ case (a, b) => a + b }) // List(3,7)  


// Now lets define a non anonymous function of the same type as above:
def  func(x: (Int,Int)) = x match {case (a,b) => a + b}

// Scala allows this readable "infix notation" for single parameter methods 
val a = list map func // List(3,7)

//Now to the main point you asked, this syntax uses the same readable form as above 
//but uses an anonymous function.  
val a = list map {case (a,b) => a + b} // List(3,7)