title: R interactive plot: show vertical line on hover
body: <p>I have been looking around for a way to draw a vertical line along the x-axis when hovering over points in a plot using R. It does not really matter which package it is, whether it is plotly, ggvis, rCharts, googleVis or any other for that matter, but I would rather use one of the these mentioned ones if possible.</p>
  
  <p>Here is an example of what I would like to have.</p>
  
  <p><kbd><a href="https://i.stack.imgur.com/MAbOM.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/MAbOM.png" alt=""></a></kbd></p>