HowTo get a Map from a csv string

Question

I'm fairly new to Scala, but I'm doing my exercises now.
I have a string like

"A>Augsburg;B>Berlin"

. What I want at the end is a map

val mymap = Map("A"->"Augsburg", "B"->"Berlin")

What I did is:

val st = locations.split(";").map(dynamicListExtract _)

with the function

private def dynamicListExtract(input: String)  = {
    if (input contains ">") {
      val split = input split ">"
      Some(split(0), split(1)) // return key , value
    } else {
      None 
    } 
  }

Now I have an

Array[Option[(String, String)

How do I elegantly convert this into a Map[String, String]

Can anybody help? Thanks

Randall Schulz · Accepted Answer · 2010-07-14 16:23:37Z

12

Just change your map call to flatMap:

scala> sPairs.split(";").flatMap(dynamicListExtract _)
res1: Array[(java.lang.String, java.lang.String)] = Array((A,Augsburg), (B,Berlin))

scala> Map(sPairs.split(";").flatMap(dynamicListExtract _): _*)
res2: scala.collection.immutable.Map[java.lang.String,java.lang.String] = Map((A,Augsburg), (B,Berlin))

For comparison:

scala> Map("A" -> "Augsburg", "B" -> "Berlin")
res3: scala.collection.immutable.Map[java.lang.String,java.lang.String] = Map((A,Augsburg), (B,Berlin))

answered Jul 14, 2010 at 16:23

Randall Schulz

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2 Comments

pr1001 Over a year ago

Another trick to know is that Map's ++ method takes a TraversaleOnce so you could use st like so: Map[String, String]() ++ st.flatMap(n => n). Randal's way is better.

Thirdman Over a year ago

Thank you for your fast answer. My problem was not the flatMap instead of map (although this is also helpful), but not knowing the <pre><code>Map(Seq(A,B) : _*) </pre></code> constructor.

Ben Lings · Accepted Answer · 2010-07-14 18:56:53Z

9

In 2.8, you can do this:

val locations = "A>Augsburg;B>Berlin"
val result = locations.split(";").map(_ split ">") collect { case Array(k, v) => (k, v) } toMap

collect is like map but also filters values that aren't defined in the partial function. toMap will create a Map from a Traversable as long as it's a Traversable[(K, V)].

answered Jul 14, 2010 at 18:56

Ben Lings

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1 Comment

Thirdman Over a year ago

I think that was I was actually looking for. Thank you!

Dave Griffith · Accepted Answer · 2010-07-14 16:42:02Z

3

It's also worth seeing Randall's solution in for-comprehension form, which might be clearer, or at least give you a better idea of what flatMap is doing.

Map.empty ++ (for(possiblePair<-sPairs.split(";"); pair<-dynamicListExtract(possiblePair)) yield pair)

answered Jul 14, 2010 at 16:42

Dave Griffith

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Comments

hbatista · Accepted Answer · 2010-07-15 08:35:42Z

0

A simple solution (not handling error cases):

val str = "A>Aus;B>Ber"
var map = Map[String,String]()

str.split(";").map(_.split(">")).foreach(a=>map += a(0) -> a(1))

but Ben Lings' is better.

answered Jul 15, 2010 at 8:35

hbatista

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Comments

Landei · Accepted Answer · 2010-07-16 10:06:56Z

0

val str= "A>Augsburg;B>Berlin"

Map(str.split(";").map(_ split ">").map(s => (s(0),s(1))):_*)

--or--

str.split(";").map(_ split ">").foldLeft(Map[String,String]())((m,s) => m + (s(0) -> s(1)))

answered Jul 16, 2010 at 10:06

Landei

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