Difference between strings in Scala while converting binary strings to integers

Question

I have a problem where I want to convert a list of 0s and 1s to an integer.

scala> val bar=List('0','1','1').toString
bar: String = List(0, 1, 1)

scala> val foo="011"
foo: String = 011

scala> Integer.parseInt(foo,2)
res1: Int = 3

scala> Integer.parseInt(bar,2)
java.lang.NumberFormatException: For input string: "List(0, 1, 1)"
        at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
        at java.lang.Integer.parseInt(Integer.java:580)
        at .<init>(<console>:9)
        at .<clinit>(<console>)
        at .<init>(<console>:7)
        at .<clinit>(<console>)
        at $print(<console>)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:498)
        at scala.tools.nsc.interpreter.IMain$ReadEvalPrint.call(IMain.scala:734)
        at scala.tools.nsc.interpreter.IMain$Request.loadAndRun(IMain.scala:983)
        at scala.tools.nsc.interpreter.IMain.loadAndRunReq$1(IMain.scala:573)
        at scala.tools.nsc.interpreter.IMain.interpret(IMain.scala:604)
        at scala.tools.nsc.interpreter.IMain.interpret(IMain.scala:568)
        at scala.tools.nsc.interpreter.ILoop.reallyInterpret$1(ILoop.scala:760)
        at scala.tools.nsc.interpreter.ILoop.interpretStartingWith(ILoop.scala:805)
        at scala.tools.nsc.interpreter.ILoop.command(ILoop.scala:717)
        at scala.tools.nsc.interpreter.ILoop.processLine$1(ILoop.scala:581)
        at scala.tools.nsc.interpreter.ILoop.innerLoop$1(ILoop.scala:588)
        at scala.tools.nsc.interpreter.ILoop.loop(ILoop.scala:591)
        at scala.tools.nsc.interpreter.ILoop$$anonfun$process$1.apply$mcZ$sp(ILoop.scala:882)
        at scala.tools.nsc.interpreter.ILoop$$anonfun$process$1.apply(ILoop.scala:837)
        at scala.tools.nsc.interpreter.ILoop$$anonfun$process$1.apply(ILoop.scala:837)
        at scala.tools.nsc.util.ScalaClassLoader$.savingContextLoader(ScalaClassLoader.scala:135)
        at scala.tools.nsc.interpreter.ILoop.process(ILoop.scala:837)
        at scala.tools.nsc.interpreter.ILoop.main(ILoop.scala:904)
        at xsbt.ConsoleInterface.run(ConsoleInterface.scala:62)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:498)
        at sbt.compiler.AnalyzingCompiler.call(AnalyzingCompiler.scala:101)
        at sbt.compiler.AnalyzingCompiler.console(AnalyzingCompiler.scala:76)
        at sbt.Console.sbt$Console$$console0$1(Console.scala:22)
        at sbt.Console$$anonfun$apply$2$$anonfun$apply$1.apply$mcV$sp(Console.scala:23)
        at sbt.Console$$anonfun$apply$2$$anonfun$apply$1.apply(Console.scala:23)
        at sbt.Console$$anonfun$apply$2$$anonfun$apply$1.apply(Console.scala:23)
        at sbt.Logger$$anon$4.apply(Logger.scala:85)
        at sbt.TrapExit$App.run(TrapExit.scala:248)
        at java.lang.Thread.run(Thread.java:745)

The parsing function works for "011" but not when the equivalent List is converted to a String. How can I convert my binary list to an integer?

Michael Zajac · Accepted Answer · 2016-08-31 21:13:39Z

3

Calling toString on any List will give you a string constructed of List(...) containing the concatenated comma-separated toStringed elements of said List. Notice how your original definition of bar returns:

bar: List(0, 1, 1)

You're looking for mkString (with no arguments in this case) that will concatenate all of the toStringed elements of the List together into one string.

scala> val bar = List('0','1','1').mkString
bar: String = 011

scala> Integer.parseInt(bar, 2)
res0: Int = 3

answered Aug 31, 2016 at 21:13

Michael Zajac

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Nathaniel Ford · Accepted Answer · 2016-08-31 21:19:17Z

2

Calling toString actually gives you a string that describes the List, not an actual String composed only of the List elements. You want mkString (in a worksheet):

val a: String = List("0","1","1").toString
a  // res0: String = List(0, 1, 1)
val b: String = List("0","1","1").mkString
b  // res1: String = 011
Integer.parseInt(b, 2)  // res2: Int = 3

Any time you see toString assume that it is providing a human-readable version of the object it was called on, describing exactly what that object is. In this case, you want a machine-readable version for Integer.parseInt() to process.

answered Aug 31, 2016 at 21:19

Nathaniel Ford

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