How to create a Map[String,String] from Map[String, Any] in Scala?

scala map any
coolgar picture coolgar · Oct 9, 2014 · Viewed 8.7k times · Source

New to scala - How to create a Map[String,String] from Map[String, Any] The values of the Map[String,Any] are strings but I don't know how to cast or otherwise coerce the "Any" type to a "String" type.

Answer

tuxdna picture tuxdna · Oct 9, 2014

As you mentioned that all the values in your map are strings, you can simply use asInstanceOf. If your assumption is incorrect, you will receive runtime exceptions as demonstrated below:

$ scala
Welcome to Scala version 2.9.2 (OpenJDK 64-Bit Server VM, Java 1.7.0_55).
Type in expressions to have them evaluated.
Type :help for more information.

scala> val m:Map[String, Any] = Map("foo" -> 5, "bar" -> 7.6, "baz" -> "qux")
m: Map[String,Any] = Map(foo -> 5, bar -> 7.6, baz -> qux)

scala> val m2: Map[String, Any] = Map("foo" -> "5", "bar" -> "7.6", "baz" -> "qux")
m2: Map[String,Any] = Map(foo -> 5, bar -> 7.6, baz -> qux)

scala> m2.asInstanceOf[Map[String, String]]
res0: Map[String,String] = Map(foo -> 5, bar -> 7.6, baz -> qux)

This is perfect when all values are actually of type String.

scala> res0("foo")
res5: String = 5

Watch out for your wrong assumption:

scala> m.asInstanceOf[Map[String, String]]
res2: Map[String,String] = Map(foo -> 5, bar -> 7.6, baz -> qux)

scala> res2("foo")
java.lang.ClassCastException: java.lang.Integer cannot be cast to java.lang.String
    at .<init>(<console>:10)
    at .<clinit>(<console>)
    at .<init>(<console>:11)
    at .<clinit>(<console>)
    at $print(<console>)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at scala.tools.nsc.interpreter.IMain$ReadEvalPrint.call(IMain.scala:704)
    at scala.tools.nsc.interpreter.IMain$Request$$anonfun$14.apply(IMain.scala:920)
    at scala.tools.nsc.interpreter.Line$$anonfun$1.apply$mcV$sp(Line.scala:43)
    at scala.tools.nsc.io.package$$anon$2.run(package.scala:25)
    at java.lang.Thread.run(Thread.java:744)

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