title: Question mark in arff file
body: <p>i'd like to know can i replace the question mark in arff file to "0"? Are there any difference? one example below:</p>
  
  <blockquote>
    <p>@data</p>
    
    <blockquote>
      <p>4.4,?,1.5,?,Iris-setosa</p>
    </blockquote>
  </blockquote>