title: In R (ggplot2) how to add arrows for binary variables that move estimate line up/down?
body: <p>Assume I do the following:</p>
  <pre><code>    # Simple scatter plot with correlation coefficient and
  # regression line
  #::::::::::::::::::::::::::::::::::::::::::::::::::::
  ggscatter(mtcars, x = &quot;wt&quot;, y = &quot;mpg&quot;, add = &quot;reg.line&quot;) +
    stat_cor(label.x = 3, label.y = 34) +
    stat_regline_equation(label.x = 3, label.y = 32)
  #&gt; `geom_smooth()` using formula 'y ~ x'
  </code></pre>
  <p>(I copied that from: <a href="https://rpkgs.datanovia.com/ggpubr/reference/stat_regline_equation.html" rel="nofollow noreferrer">https://rpkgs.datanovia.com/ggpubr/reference/stat_regline_equation.html</a>)</p>
  <p>However, my model is not only (x= wt and y= mpg) I also have 3 dummies, say CABRIO (0/1) and MPV (0/1) and SUV (0/1) (assume here, they are mutually exclusive (each car is only one of the dummies or a left-out category), interactions impossible!). I add them linearly in the model, so they just change the slope:
  mpg = b1* wt + b2 * CABRIO + b3 * MPV + b4 * SUV.</p>
  <p>Instead of plotting lines for all the possible body types (SUV/MPV/Cabriolet) I want arrows showing in which the &quot;baseline&quot; would shift with arrows in the size of the effect.</p>
  <p>Is this possible in GGPLOT?</p>
  <p>I added a (very bad) picture <a href="https://i.stack.imgur.com/VD1pe.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/VD1pe.png" alt="see for exaple" /></a>  , that shows what I want. I want arrows on the line the size of the beta coefficients (b2, b3,b4).</p>