title: Mapdist: Error is.character(from)
body: <p>My dataset includes a column "pickup" corresponding to the starting coordinates and a "dropoff" for the ending coordinates, of a trip. Like:</p>
  
  <pre><code>pickup                 dropoff 
  40.77419,-73.872608    40.78055,-73.955042
  40.7737,-73.870721     40.757007,-73.971953
  </code></pre>
  
  <p>I want to calculate the shortest route suggested by Google Maps, and saved the calculations in a new column. This is what I'm doing:</p>
  
  <pre><code> X$GoogleDist &lt;- mapdist(from= list(X$pickup), 
      to = list(X$dropoff), 
      mode = "driving" ,
      output = "simple", messaging = FALSE, sensor = FALSE,
      language = "en-EN", override_limit = FALSE)
  </code></pre>
  
  <p>Which gives me the following error:</p>
  
  <pre><code>  Error: is.character(from) is not TRUE
  </code></pre>