title: How can I add a horizontal line over the x axis in R?
body: <p>I'm trying to add  a red line over the x axis of a plot in R.</p>
  
  <p>I have:</p>
  
  <pre><code>    plot(model$res, model$fit, xlab = expression(hat(y)), 
           ylab = 'Residusals', 
           main = 'Residuals vs. Predicted',
           pch = 4, col = 'red')
      abline(h = 0, col = 'red')
  </code></pre>
  
  <p>However, the line is not drawn over the x axis. I'd prefer not to delete or change the color of the axis if possible.</p>