title: Converting a column of type 'list' to multiple columns in a data frame
body: <p>I have a data frame with one column which is a list, like so:</p>
  
  <pre><code>&gt;head(movies$genre_list)
  [[1]]
  [1] "drama"   "action"  "romance"
  [[2]]
  [1] "crime" "drama"
  [[3]]
  [1] "crime"   "drama"   "mystery"
  [[4]]
  [1] "thriller" "indie"  
  [[5]]
  [1] "thriller"
  [[6]]
  [1] "drama"  "family"
  </code></pre>
  
  <p>I want to convert this one column to multiple columns, one for each unique element across the lists (in this case, genres), and have them as binary columns. I'm looking for an elegant solution, which doesn't involve first finding out how many genres are there, and then creating a column for each, and then checking each list element to then populate the genre columns. I tried unlist, but it doesn't work with a vector of lists in the way I want. </p>
  
  <p>Thanks!</p>