title: How to make the line fragments match up to single points in ggplot
body: <p>I am currently trying to make a plot that shows before and after data of some ants based on site, however  ggplot keeps connecting all the points rather than doing it by unique site.</p>
  
  <p>I've attached my code below, and a snippet of my data. I simply want one line fragment to connect two points.</p>
  
  <pre><code>  NumofAnts  Foodtype Trial
  1         0 Pink.sum.     1
  2         5 Pink.sum.     1
  3         4 Pink.sum.     1
  4         2 Pink.sum.     2
  5        36 Pink.sum.     2
  6         0 Pink.sum.     2
  &gt; 
  
  `ggplot(winter_pre_post2, aes(x=Trial, y=NumofAnts, group=Foodtype)) +
    geom_point(aes(colour=Foodtype), size=4.5, position=position_dodge(width=0.1)) +
    geom_line(size=1, alpha=0.5, position=position_dodge(width=0.1)) +
    xlab('Trial') +
    ylab('Number of Ants')+
    scale_colour_manual(values=c('Pink', "skyblue", "forestgreen", "yellow","red"), guide=FALSE) + 
    theme_bw()`
  </code></pre>