CODEWITHSUNDEEP
performancelistscalacollectionstime-complexity
More Than Five
More Than Five

Reputation: 10419

Difference between sorted and sortBy

According to doc for List

def  sorted[B >: A](implicit ord: math.Ordering[B]): List[A] 
Sorts this list according to an Ordering.


def sortBy[B](f: (A) ⇒ B)(implicit ord: math.Ordering[B]): List[A]

Sorts this List according to the Ordering which results from transforming an implicitly given Ordering with a transformation function.

When would you use one and when would you use the other? Does one cover a scenario the other does not?

Upvotes: 4

Views: 258

Answers (3)

Debilski
Debilski

Reputation: 67878

You would use sorted with an Ordering if you have to consider multiple cases. Suppose we want to sort the following list having shortest strings at the beginning.

val xs = "aa" :: "b" :: "bb" :: "a" :: Nil

xs.sortBy(_.length)
> List[String] = List(b, a, aa, bb)

If we want to additionally sort them alphabetically, when they have the same length, we could use sorted

xs.sorted(math.Ordering[(Int, String)].on((x: String) => (x.length, x)))
> List[String] = List(a, b, aa, bb)

But then again, we could have used

xs.sortBy(x => (x.length, x))
> List[String] = List(a, b, aa, bb)

as well.

The idea is that you can supply Ordering type classes for your own types and then a simple xs.sorted with such an implicit Ordering will work for the most common use cases.

Upvotes: 3

om-nom-nom
om-nom-nom

Reputation: 62835

For sortBy you can supply custom function that produces elements used for sorting (e.g. sort by the length string) whereas for sorted you cant:

val xs = List("aa", "b")
// xs: List[String] = List(aa, b)
xs.sortBy{ str => str.length }
// List[String] = List(b, aa)

// now usual lexicographical sorting
xs.sorted
// List[String] = List(aa, b)
xs.sortBy(x => x)
// List[String] = List(aa, b)
xs.sortBy(identity)
// List[String] = List(aa, b)

as you can see, last three lines are identical in their result

Upvotes: 6

ValarDohaeris-fuck-OpenAI
ValarDohaeris-fuck-OpenAI

Reputation: 6308

As a complement to @om-nom-nom's answer, here is an example of typical usage of the two:

val xs = List(4, 2, 3, 1)
val ys = List((1, 1), (3, 2), (2, 3))
println(xs.sorted)       // List(1, 2, 3, 4)
println(ys.sortBy(_._1)) // List((1,1), (2,3), (3,2))

Upvotes: 0

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