title: Regular expression that both includes and excludes certain strings in R
body: <p>I am trying to use R to parse through a number of entries. I have two requirements for the the entries I want back. I want all the entries that contain the word <code>apple</code> but don't contain the word <code>orange</code>.</p>
  
  <p>For example:</p>
  
  <ol>
  <li>I like apples  </li>
  <li>I really like apples  </li>
  <li>I like apples and oranges  </li>
  </ol>
  
  <p>I want to get entries 1 and 2 back.</p>
  
  <p>How could I go about using R to do this?</p>
  
  <p>Thanks.</p>