What is the most efficient way to transform of seq of X to a seq of Y-CodePudding

I have a Seq of objects like Seq(x1, x2, x3, x4) and I want to tranform it to Seq(y1, y2, y3, y4)

What is the most efficient way of doing so

Right now I am

val seq1 = Seq(x1, x2, x3......)
var seq2 = Seq[MyType2]()



for (myObj <- seq1) {
    seq2 = seq2 :  myObj.tranformToType2
}

The problem is that the scala doc says

https://www.scala-lang.org/api/2.12.x/scala/collection/Seq.html

a new sequence consisting of all elements of this sequence followed by elem.

so I was wondering what is the most idiomatic/efficient way of tranforming a list of object to another list of object

CodePudding user response：

The code you wrote is Scala imperative style, but Scala aims to be a functional language.

The functional approach being:

val seq2 = seq1.map(myObj => myObj.tranformToType2)

// Or shorter:
val seq2 = seq1.map(_.tranformToType2)

map is one of the most useful operation in function programming. You will see that you'll use it everywhere when you need to transform something into something else.

As a rule of thumb, whenever you see a var and a for loop, this is smelly and you should ask yourself how do I do this the functional way?

CodePudding user response：

map is the function that you are looking for. Check the docs for details.

A simplistic example:

case class MyType1(x: String)
case class MyType2(x: Int)

val ls: Seq[MyType2] = Seq(MyType1("hello"), MyType1("world")).map(mt1 => MyType2(mt1.content.length))