title: Comparision of these types not implemented R
body: <p>I have two data frames with a column as factors and i am trying to compare them both but it's resulting in an error. What i am doing wrong in here ? The comparison works for element 0 though </p>
  
  <pre><code> Browse[2]&gt; meta['Strip.']
            Strip.
      1 01/03/2017
      2 01/07/2017
      3 01/11/2017
      4 01/05/2017
      Browse[2]&gt; opts['Strip.']
            Strip.
      1 01/03/2017
      2 01/07/2017
      3 01/11/2017
      4 01/05/2017
      Browse[2]&gt; opts[4,'Strip.'] 
      [1] 01/05/2017
      Levels: 01/03/2017 01/05/2017 01/07/2017 01/11/2017
      Browse[2]&gt; meta[4,'Strip.'] 
      [1] 01/05/2017
      Levels: 01/03/2017 01/05/2017 01/07/2017 01/11/2017
      Browse[2]&gt; meta['Strip.'] == opts[4,'Strip.'] 
      Error in meta["Strip."] == opts[4, "Strip."] : 
        comparison of these types is not implemented
      In addition: Warning message:
      Incompatible methods ("Ops.data.frame", "Ops.factor") for "==" 
  </code></pre>
  
  <p>My Full comparison to extract the same line and i have for loop to iterate through i. </p>
  
  <pre><code>  meta.line &lt;- meta[ meta['Strip.'] == opts[i, 'Strip.'] &amp;meta['Contract_type.'] == opts[i, 'Contract_type.'] &amp; meta['Strike.'] == opts[i,'Strike.'], ]
  </code></pre>