title: Why is object of type 'closure' is not subsettable?
body: <p>I have tried the code two months ago and it worked back then, but now it won't work. </p>
  
  <p>This is the code:</p>
  
  <pre><code>summary(example[, 1:3] )
  </code></pre>
  
  <blockquote>
    <p>error in example[, 1:3] : object of type 'closure' is not subsettable</p>
  </blockquote>
  
  <p>I have several other codes with <code>[]</code> and they give the same error.</p>