title: Why subset doesn't mind missing subset argument for dataframes?
body: <p>Normally I wonder where mysterious errors come from but now my question is where a mysterious lack of error comes from.</p>
  
  <p>Let</p>
  
  <pre><code>numbers &lt;- c(1, 2, 3)
  frame &lt;- as.data.frame(numbers)
  </code></pre>
  
  <p>If I type</p>
  
  <pre><code>subset(numbers, )
  </code></pre>
  
  <p>(so I want to take some subset but forget to specify the subset-argument of the subset function) then R reminds me (as it should):</p>
  
  <blockquote>
    <p>Error in subset.default(numbers, ) :<br>
    argument "subset" is missing, with no default</p>
  </blockquote>
  
  <p>However when I type</p>
  
  <pre><code>subset(frame,)
  </code></pre>
  
  <p>(so the same thing with a <code>data.frame</code> instead of a vector), it doesn't give an error but instead just returns the (full) dataframe.</p>
  
  <p>What is going on here? Why don't I get my well deserved error message?</p>