title: How do I format the names of the variables in the R plotly tooltip?
body: <p>I have been trying to make a map of the U.S. with a superimposed scatterplot of shootings with both the number of people killed and injured in the hoverinfo label of each point. However, the label pops up as "num_killed" and I would like to format this as "Number Killed: ". So far, I have tried labeling the variables in the ggplot section, to no avail. Is there any way to change how the variable name is printed in the tooltip? </p>
  
  <p>Here is my code:</p>
  
  <pre><code>library(plotly)
  library(dplyr)
  library(ggplot2)
  
  us &lt;- map_data("state")
  library(maps)
  
  g &lt;- ggplot() +
    geom_polygon(data = us, aes(x=long, y = lat, group = group), fill="grey", alpha=0.3) +
    geom_point(data=shootings, aes(x=lng, y=lat, size = num_killed, color = num_injured)) +
    labs(color = "Number Injured", size = "Number Killed", num_killed = "Number Killed", num_injured = "Number Injured")
  plot &lt;- ggplotly(g)
  </code></pre>
  
  <p>Here is the result:
  <a href="https://i.stack.imgur.com/WwXWE.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/WwXWE.png" alt="Image showing tooltip"></a></p>
  
  <p>Dataset attached is the processed csv of this database: <a href="http://www.gunviolencearchive.org/reports/mass-shooting?page=1" rel="nofollow noreferrer">http://www.gunviolencearchive.org/reports/mass-shooting?page=1</a>
  (processed as data frame).</p>