title: Update a Value in One Column Based on Criteria in Other Columns
body: <p>If my data frame (df) looks like this: </p>
  
  <pre><code>Name        State
  John Smith  MI
  John Smith  WI
  Jeff Smith  WI
  </code></pre>
  
  <p>I want to rename the John Smith from WI "John Smith1".  What is the cleanest R equivalent of the SQL statement?</p>
  
  <pre><code>update df 
  set Name = "John Smith1"
  where Name = "John Smith"
  and State = "WI"
  </code></pre>