Combining / uniting two strings in Scala

Question

What would be the best way to combine "__L_" and "_E__" to "_EL_" in Scala?

I don't want to use if and for commands.

def combine(x: String, y: String) = "EL". But seriously, your problem is severely underspecified. — Sean
– Sean, Commented Nov 21, 2015 at 8:27
@JulleImmonen you should add that description to the question body — Zavior
– Zavior, Commented Nov 21, 2015 at 9:12
@JulleImmonen what if both symbols are defined at specific position? — Odomontois
– Odomontois, Commented Nov 21, 2015 at 9:37
Please edit your question to clarify what you mean. Are you looking to concatenate two strings, without the last character of the first and the first character of the second? Or do you need to check that last/first characters are from some set of "hidden letters"? Or that they match? Really, you've not explained your problem yet. — The Archetypal Paul
– The Archetypal Paul, Commented Nov 21, 2015 at 9:38

Rüdiger Klaehn · Accepted Answer · 2015-11-21 11:37:35Z

3

How about this:

def combine(xs: String, ys: String): String = 
  (xs zip ys).map {
    case ('_', y) => y
    case (x, _) => x 
  }.mkString("")

The only thing that is not really nice about this is how to get back from a collection (IndexedSeq[Char]) to a string. An alternative is to use the String constructor that takes an Array[Char]. That would probably be more efficient.

Note that zip will work for strings of different length, but the result will be the size of the shorter string. This may or may not be what you want.

edited Nov 21, 2015 at 11:37

answered Nov 21, 2015 at 9:27

Rüdiger Klaehn

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6 Comments

Odomontois Over a year ago

Sorry it's my accidental misclick downvote. If you will do some minor edit to your answer I will able to remove it.

The Archetypal Paul Over a year ago

My downvote wasn't accidental :) combine("_E_", "_L_") //> res0: String = _E_ is not a desirable outcome

Rüdiger Klaehn Over a year ago

What would be the desirable outcome in that case?

The Archetypal Paul Over a year ago

"-EL-". The OP even gives that as an example in a comment (using-, not _ because _ gets eaten by the markdown)

Nebril Over a year ago

@TheArchetypalPaul Your donwvote should have been accidental. The words from example have 4 chars.

|

Odomontois · Accepted Answer · 2015-11-21 10:54:23Z

2

def zipStrings(first: String,
               second: String,
               comb: (Char, Char) => String = (f, _) => f.toString, 
               placeholder: Char = '_') =
  first.zipAll(second, '_', '_').map {
  case (c, `placeholder`) => c
  case (`placeholder`, c) => c
  case (f, s) => comb(f, s)
}.mkString

that prioritises characters from first over second by default

zipStrings("__A", "X_CD") // yields "X_AD"

zipStrings("A__YY", "BXXXX", (f, s) => s"($f|$s)") // yields "(A|B)XX(Y|X)(Y|X)"

For you original strings:

zipStrings("L_", "_E")  // yield "LE"

zipStrings("--L-", "-E--", placeholder = '-') // yields "-EL-"

edited Nov 21, 2015 at 10:54

answered Nov 21, 2015 at 9:42

Odomontois

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4 Comments

The Archetypal Paul Over a year ago

It would be good to give examples for the OP's two test cases zipStrings("E_", "_L") //> res0: String = EL works, but zipStrings("_E_", "_L_") //> res1: String = _E_ doesn't. Maybe I'm invoking it incorrectly though.

Odomontois Over a year ago

@TheArchetypalPaul You misreaded the second example it's "--L-" and "-E--" => "-EL-".

The Archetypal Paul Over a year ago

yes, I missed that. But now I think it's really unclear what the requirement is. Reversed the downvote, but I think the various answers (including mine) show the futility of trying to guess what the OP meant...

Nebril Over a year ago

This reminds me of a thing I saw sometime about overcomplicated solutions: synflood.at/blog/index.php?/archives/… :)

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