Better way to parse string to associative array in Scala?

Question

I currently have the following, which works, but I'm very new to Scala and I'm wondering if there's a better way to do it.

val utmcsr = """.*utmcsr=(.*)""".r
val utmcmd = """.*utmcmd=(.*)""".r
val utmccn = """.*utmccn=(.*)""".r
val utmctr = """.*utmctr=(.*)""".r

val utmz = "14002953.138298057.2.2.utmcsr=google|utmccn=(organic)|utmcmd=organic|utmctr=(not%20provided)"
utmz.split("""\|""").map {
        case utmcsr(s) => List("utmscr", s)
        case utmcmd(s) => List("utmcmd", s)
        case utmccn(s) => List("utmccn", s)
        case utmctr(s) => List("utmctr", s)
        case _ => ""
    }.foldLeft(Map[String,String]()) {
        (m, s) => 
            val key = s.asInstanceOf[List[String]].head
            val value = s.asInstanceOf[List[String]].tail.head
            m + (key -> value)
    }
}

My main questions are:

Why do I need to parse s as an instance of List - shouldn't it already be a list?
Is there a way to do this with tuples instead of lists?
Is there a built-in way to do the list to map conversion?

Can you show at least one definition of extractors? e.g. utmcsr — om-nom-nom
– om-nom-nom, Commented Nov 22, 2013 at 16:18

om-nom-nom · Accepted Answer · 2013-11-22 16:30:00Z

5

All your code can be written in the following way:

val kv = """.*(utmcsr|utmcmd|utmccn|utmctr)=(.*)""".r
// assuming you don't want to do this generally, only utmcsr ... utmctr values are accepted
// otherwise there can be something like """.*([a-z]+)=(.*)""".r
val utmz = "14002953.138298057.2.2.utmcsr=google|utmccn=(organic)|utmcmd=organic|utmctr=(not%20provided)"

utmz.split("""\|""").map {
    case kv(key, value) => key -> value
}.toMap
// Map(utmcsr -> google, utmccn -> (organic), utmcmd -> organic, utmctr -> (not%20provided))

Now answering your questions:

Why do I need to parse s as an instance of List - shouldn't it already be a list?

Because of default case -- empty string is not a List. Questions 2 and 3 demonstrated in snippet above.

P.S. if you want to silently ignore tokens that do not match kv regexp, swap map with a collect operation. Current implementation will die with MatchError

answered Nov 22, 2013 at 16:30

om-nom-nom

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2 Comments

Erty Seidohl Over a year ago

Oh! So if I returned List("", "") for the empty case, I wouldn't have had to coerce the types in the folding?

om-nom-nom Over a year ago

@Erty exactly (and it's easy to check)

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