title: How to change factor labels into string in a data frame
body: <p>I have the following data frame:</p>
  
  <pre><code>    name1  name2
          A      B
          B      D
          C      C
          D      A
  </code></pre>
  
  <p>the columns "name1" and "name2" are treated as factors and therefore A, B, C, and D are treated as levels. However I want to somehow convert this data frame so that it become</p>
  
  <pre><code>    name1  name2
        "A"    "B"
        "B"    "D"
        "C"    "C"
        "D"    "A"
  </code></pre>
  
  <p>In other words, convert it in a way that A, B, C, and D are treated as string.</p>
  
  <p>how can i do that?</p>