title: How to add mean line in a boxplot made with highcharter?
body: <p>I'm trying to add the average (mean) in the tooltip on the boxplot made with {highcharter} the mean. By default, it displays : min, max, Q1, Q3 and median.
  I already asked SO here:<br />
  <a href="https://stackoverflow.com/questions/67120145/how-to-add-mean-in-a-boxplot-made-with-highcharter">How to add mean in a boxplot made with highcharter?</a></p>
  <p>But now I would like to display the mean with a line !
  I saw this in JS :<br />
  <a href="https://www.javaer101.com/en/article/95104988.html" rel="nofollow noreferrer">https://www.javaer101.com/en/article/95104988.html</a></p>
  <p>And I think I'm closed with {highcharter} in my example below.</p>
  <p>Many thanks in advance !</p>
  <pre><code>library(dplyr)
  library(highcharter) 
  
  data(pokemon) 
  
  pokemon_graph &lt;- pokemon %&gt;% 
    group_by(type_1) %&gt;% 
    mutate(moyenne = round(mean(height,na.rm = T)),1) %&gt;% 
    ungroup()
  
  dat &lt;- data_to_boxplot(pokemon_graph, height, type_1, name = &quot;height in meters&quot;)
  
  highchart() %&gt;%
    hc_xAxis(type = &quot;category&quot;) %&gt;%
    hc_add_series_list(dat) %&gt;% 
    hc_tooltip(useHTML = TRUE, headerFormat = &quot;&lt;strong&gt;mon graph&lt;/strong&gt;&lt;br/&gt;&quot;,
               pointFormat = paste0(&quot;Min: {point.low}&lt;br/&gt;
                                     Q1: {point.q1}&lt;br/&gt;
                                     Median: {point.median}&lt;br/&gt;
                                     Q3: {point.q3}&lt;br/&gt;
                                     Max: {point.high}&lt;br/&gt;
                                     Mean: {point.moyenne}&lt;br/&gt;&quot;))
  </code></pre>
  <p><a href="https://i.stack.imgur.com/wXl53.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/wXl53.png" alt="enter image description here" /></a></p>