title: Dataset in base R with missing values
body: <p>Are there any examples of dataset in base R that contain missing values? I've been looking through each one in turn and also searched using google-nothing so far. </p>
  
  <pre><code>library(MASS)
  data()
  </code></pre>
  
  <p>Edit: I know how to add missing values to a dataset in R, I just want to know if any such datasets exist.</p>