Can I return Map collection in Scala using for-yield syntax?

Question

I'm fairly new to Scala, so hopefully you tolerate this question in the case you find it noobish :)

I wrote a function that returns a Seq of elements using yield syntax:

def calculateSomeMetrics(names: Seq[String]): Seq[Long] = {

  for (name <- names) yield {

    // some auxiliary actions

    val metrics = somehowCalculateMetrics()

    metrics

  }

}

Now I need to modify it to return a Map to preserve the original names against each of the calculated values:

def calculateSomeMetrics(names: Seq[String]): Map[String, Long] = { ... }

I've attempted to use the same yield-syntax but to yield a tuple instead of a single element:

def calculateSomeMetrics(names: Seq[String]): Map[String, Long] = {

  for (name <- names) yield {

    // Everything is the same as before

    (name, metrics)

  }

}

However, the compiler interprets it

Seq[(String, Long)]

, as per the compiler error message

type mismatch;

  found   : Seq[(String, Long)]

  required: Map[String, Long]

So I'm wondering, what is the "canonical Scala way" to implement such a thing?

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Answer 1

Either:

def calculateSomeMetrics(names: Seq[String]): Map[String, Long] = {
  (for (name <- names) yield {
    // Everything is the same as before
    (name, metrics)
  }).toMap
}

Or:

names.map { name =>
  // doStuff
  (name, metrics)
}.toMap

Can I return Map collection in Scala using for-yield syntax?

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