title: How to use grep()/gsub() to find exact match
body: <pre><code>string = c("apple", "apples", "applez")
  grep("apple", string)
  </code></pre>
  
  <p>This would give me the index for all three elements in <code>string</code>. But I want an exact match on the word "apple" (i.e I just want <code>grep()</code> to return index 1).  </p>