title: How can I read a CSV file and put its content in a Map in Scala?
body: <p>I have a CSV file, which contains a data matrix. The first column of this matrix contains a label and the other columns contain values, which are associated to the label (i.e. to the first column). Now I want to read this CSV file and put the data into a Map[String,Array[String]] in Scala. The key of the Map should be the label (this in the first column) and the Map values should be the other values (these one in the rest of the columns). To read the CSV file I use opencsv.  </p>
  
  <pre><code>val isr: InputStreamReader = new InputStreamReader(getClass.getResourceAsStream("test.csv"))`  
  val data: IndexedSeq[Array[String]] = new CSVReader(isr).readAll.asScala.toIndexedSeq`
  </code></pre>
  
  <p>Now I have all data in an <code>IndexedSeq[Array[String]]</code>. Can I use this functional way here or should I better chose an iterative way, because it can get complex to read all data at once? Well, now I need to create the Map from this IndexedSeq. Therefor I map the IndexedSeq to an IndexedSeq of <code>Tupel[String,Array[String]]</code> to seperate the label value from the rest of the values and then I create the Map from this.</p>
  
  <pre><code>val result: Map[String, Array(String) = data.filter(e =&gt; !e.isEmpty).map(e =&gt; (e.head,e.tail)).toMap
  </code></pre>
  
  <p>This works for small examples but when I use it to read the content of my CSV file it throws a java.lang.RuntimeException. I also tried to create the map with a groupBy or to create several Maps (one for each line) and to reduce them afterwards to one big Map, but without success. I also read another post on stackoverflow and somebody assumes that toMap has a complexity of O(n²). I got this at the end of my StackTrace (whole Stacktrace is quite long).</p>
  
  <pre><code>Exception in thread "main" java.lang.reflect.InvocationTargetException      
      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:601)
      at org.jetbrains.plugins.scala.testingSupport.specs2.JavaSpecs2Runner.runSingleTest(JavaSpecs2Runner.java:130)  
      at org.jetbrains.plugins.scala.testingSupport.specs2.JavaSpecs2Runner.main(JavaSpecs2Runner.java:76)  
      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:601)  
      at com.intellij.rt.execution.application.AppMain.main(AppMain.java:120)  
      Caused by: java.lang.RuntimeException: can not create specification: com.test.MyClassSpec  
      at scala.sys.package$.error(package.scala:27)  
      at org.specs2.specification.SpecificationStructure$.createSpecification(BaseSpecification.scala:96)   
      at org.specs2.runner.ClassRunner.createSpecification(ClassRunner.scala:64)  
      at org.specs2.runner.ClassRunner.start(ClassRunner.scala:35)  
      at org.specs2.runner.ClassRunner.main(ClassRunner.scala:28)  
      at org.specs2.runner.NotifierRunner.main(NotifierRunner.scala:24)  
      ... 11 more  
      Process finished with exit code 1
  </code></pre>
  
  <p>Does anybody know another way to create a Map from the data in a CSV file?</p>