Efficiently repeat a character/string n times in Scala

string scala char concatenation string-concatenation
TimY picture TimY · Jul 26, 2015 · Viewed 28.7k times · Source

I would like to do the following more efficiently:

def repeatChar(char:Char, n: Int) = List.fill(n)(char).mkString
def repeatString(char:String, n: Int) = List.fill(n)(char).mkString

repeatChar('a',3)     // res0: String = aaa
repeatString("abc",3) // res0: String = abcabcabc

Answer

Travis Brown picture Travis Brown · Jul 26, 2015

For strings you can just write "abc" * 3, which works via StringOps and uses a StringBuffer behind the scenes.

For characters I think your solution is pretty reasonable, although char.toString * n is arguably clearer. Do you have any reason to suspect the List.fill version isn't efficient enough for your needs? You could write your own method that would use a StringBuffer (similar to * on StringOps), but I would suggest aiming for clarity first and then worrying about efficiency only when you have concrete evidence that that's an issue in your program.

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