title: Scala Convert [Seq[string] to [String]? (TF-IDF after lemmatization)
body: <p>I try to learn scala and specificaly text minning (lemmatization ,TF-IDF matrix and LSA).</p>
  
  <p>I have some texts i want to lemmatize and make a classification (LSA). I use spark on cloudera.</p>
  
  <p>So i used the stanfordCore NLP fonction:</p>
  
  <pre><code>    def plainTextToLemmas(text: String, stopWords: Set[String]): Seq[String] = {
      val props = new Properties()
      props.put("annotators", "tokenize, ssplit, pos, lemma")
      val pipeline = new StanfordCoreNLP(props)
      val doc = new Annotation(text)
      pipeline.annotate(doc)
      val lemmas = new ArrayBuffer[String]()
      val sentences = doc.get(classOf[SentencesAnnotation])
      for (sentence &lt;- sentences; token &lt;-sentence.get(classOf[TokensAnnotation])) {
      val lemma = token.get(classOf[LemmaAnnotation])
      if (lemma.length &gt; 2 &amp;&amp; !stopWords.contains(lemma)) {
      lemmas += lemma.toLowerCase
      }
      }
      lemmas
      }
  </code></pre>
  
  <p>After that, i try to make an TF-IDF matrix but here is my problem:
  The Stanford fonction make an RDD in [Seq[string] form.
  But, i have an error.
  I need to use a RDD in [String] form (not the [Seq[string]] form).</p>
  
  <pre><code>val (termDocMatrix, termIds, docIds, idfs) = termDocumentMatrix(lemmatized-text, stopWords, numTerms, sc)
  </code></pre>
  
  <p>Someone know how convert a [Seq[string]] to [String]?</p>
  
  <p>Or i need to change one of my request?.</p>
  
  <p>Thanks for the help.
  Sorry if it's a dumb question and for the english.</p>
  
  <p>Bye</p>