title: R: draw a line between two points in ggplot
body: <p>I have a data frame looks like this one:</p>
  
  <pre><code>X      Y
  100    50
  80     60
  70     90
  110    60
  30     20
  ... ...
  </code></pre>
  
  <p>Around 100 lines more. Both X column and Y column are numeric</p>
  
  <p>When I plot this points, I would like to draw a line between first point (100,50) and any of the rest points. In other words, I would like to have a line connects (100,50) with (80,60), a line connects (100,50) with (70,90), a line connects (100,50) with (110,60) but there is no line between (80,60) and (70,90). All lines start from the first point.</p>
  
  <p>I do not have the third column. I can not use group. I wonder whether I can still plot this graph in the ggplot. </p>
  
  <p>Thank you</p>