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Editorial Team
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Asked: 2026-05-26T10:52:18+00:00

The List object has the mkString method that will can convert to a string

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The List object has the mkString method that will can convert to a string with a seperator. However most human languages treats the last element different when enumerating a list. For example A, B, C and D.

What is the best in terms of code size and reasonable efficiency to accomplish this? To be precise, I am searching for a function that satisfies:

assertEquals("",foo(List()))
assertEquals("A",foo(List("A")))
assertEquals("A and B",foo("List("A","B")))
assertEquals("A, B and C", foo(List("A","B","C")))
assertEquals("A, B, C and D", foo(List("A","B","C","D")))
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1 Answer

  1. Editorial Team
    def foo(xs: List[String]) = 
  (xs.dropRight(2) :\ xs.takeRight(2).mkString(" and "))(_+", "+_)

    edit: This might be a bit clearer:

    def foo(xs: List[String]) = 
  (xs.dropRight(2) :+ xs.takeRight(2).mkString(" and ")).mkString(", ")

    @axaluss The speed depends on the list length. With an average list length above about 4 elements, this second version is faster than Tomasz’s. Otherwise, it’s slightly slower.

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