title: Weka: Train and test set are not compatible
body: <p>I'm trying to classify some web posts using weka and naive bayes classifier.</p>
  
  <p>First I manually classified many posts (about 100 negative and 100 positive) and I created an .arff file with this form:</p>
  
  <pre><code>@relation classtest
  @attribute 'post' string
  @attribute 'class' {positive,negative}
  @data
  'RT @burnreporter: Google has now indexed over 30 trillion URLs. Wow. #LeWeb',positive
  'A special one for me  Soundcloud at #LeWeb ',positive
  'RT @dianaurban: Lost Internet for 1/2 hour at a conference called #LeWeb. Ironic, yes?',negative
     .
     .
     .
  </code></pre>
  
  <p>Then I open <em>Weka Explorer</em> loading that file and applying the <code>StringToWordVector</code> filter to split the posts in single word attributes.</p>
  
  <p>Then, after doing the same with my dataset, selecting (in classify tab of weka) <code>naive bayes</code> classifier and choosing select test set, it returns <code>Train and test set are not compatible</code>. What can I do? Thanks!</p>