title: How to add the diagonal line in depended vs predict plot in R
body: <p>I performed regression analysis.
  Now i need create plot <code>depended vs prediction</code>, where depend is initial values of dependent var(mpg) and predict is predicted values.</p>
  
  <pre><code> house_test=lm(mpg ~ 1 + hp + wt, data=mtcars)
  
  prediction &lt;- as.data.frame(predict(house_test, mtcars, 
                                      interval = 'prediction',
                                      level = .95))
  
  
  prediction$mpg &lt;- mtcars$mpg
  
  
  ggplot(prediction) +
    geom_ribbon(aes(mpg, ymin = lwr, ymax = upr), fill = 'lightskyblue', alpha = 0.5) +
  
    geom_point(aes(mpg, fit), alpha = 0.2) +
    labs(title = "interval 95%CI", y = "depend", x = "predict")
  </code></pre>
  
  <p>How can i add the  diagonal line(yellow color) in  depended vs predict plot?
  Note Y axis is dependent var and X asis is prediction values.</p>
  
  <p>i expect in output
  <a href="https://i.stack.imgur.com/uZkHo.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/uZkHo.jpg" alt="plot dep-pred"></a></p>