title: How to check if object (variable) is defined in R?
body: <p>I'd like to check if some variable is defined in R - without getting an error. How can I do this?</p>
  
  <p>My attempts (not successful):</p>
  
  <pre><code>&gt; is.na(ooxx)
  Error: object 'ooxx' not found
  &gt; is.finite(ooxx)
  Error: object 'ooxx' not found
  </code></pre>
  
  <p>Thanks!</p>