title: transpose long to wide within groups with tidyverse
body: <p>I cant quite work this one out.
  How do I go from:</p>
  
  <pre><code>Visit Test
  1     A
  1     B
  2     A
  2     C
  3     B
  </code></pre>
  
  <p>To:</p>
  
  <pre><code>Visit A     B     C
  1     TRUE  TRUE  FALSE
  2     TRUE  FALSE TRUE
  3     FALSE TRUE  FALSE
  </code></pre>