title: How to eliminate the through-line from a legend element in R using ggplot
body: <p>I'm having trouble eliminating a black through-line from an element in my legend. The black line is in the "% of Hires by Casual Users" element.</p>
  
  <p>Below is my code, followed by a link to the output plot</p>
  
  <p>EDIT - please note that I've added code to reproduce the problem elsewhere. This data is random and the output will not look the same as the visual below. However, it returns the same problem and can be used with the original code.  </p>
  
  <pre><code>Account.type &lt;- c("Casual", "Member", "Casual", "Member", "Casual", "Member", "Casual", "Member", "Casual", "Member")
  how &lt;- c(0, 10, 25, 35, 50, 60, 75, 100, 125, 150)
  hire &lt;- c(4540, 6780, 9125, 1000, 6993, 5435, 2347, 0693, 5434, 5432)
  cas_percent &lt;- c(34, 65, 54, 12, 65, 78, 89, 76, 54, 43)
  plot_data &lt;- data.frame(Account.type, how, hire, cas_percent)
  
  
      #plot x (time)
      plot &lt;- ggplot(data = plot_data,
                     aes(x = how)) 
  
      #plot percent casuals
      plot &lt;- plot + geom_ribbon(aes(ymin = 0, ymax = (cas_percent), fill = "% of Hires by Casual Users"), colour = "transparent", alpha = .5, show.legend = TRUE) 
  
      #plot hires 
      plot &lt;- plot + geom_line(aes(y = hire/100, colour = Account.type), size = .8, show.legend = T)
  
      #fill aes 
      plot &lt;- plot +   scale_fill_manual(name = '',  values=c("% of Hires by Casual Users" = "grey")) 
  
      #visualise
      plot
  
      #add title
      plot &lt;- plot + labs(
        title = "Who Uses the Twin City Bike Share?", 
        y = "Hires (100's)",
        x = "Day of Week")
  
      #adjust x axis 
      plot &lt;- plot + scale_x_continuous(
        breaks = c(0, 24, 48, 72, 96, 120, 144),
        label = c("Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday")) + 
        theme(axis.text.x = element_text(hjust=-0.05))
  
      #adjust right y axis
      plot &lt;- plot + scale_y_continuous(sec.axis = sec_axis(~.*1, name = "Percent of Hires by Casual Users [%]"))
  
      #visualise
      plot
  </code></pre>
  
  <p>Output: 
  <a href="https://i.stack.imgur.com/6607p.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/6607p.png" alt="enter image description here"></a></p>
  
  <p>Any suggestions on how I fix the legend? </p>