title: How to plot three or more variables in a single scatterplot with automated equations?
body: <p>I want to plot 2 variables from 3 different dataframes in one scatterplot and also plot the equations of each linear relationship automatically. I am using the following code. However I have two problems:</p>
  
  <ol>
  <li><p>I get the plots for the same values and not for the whole range (e.g. <code>df1 =700</code> values, <code>df2= 350</code> values, <code>df3=450</code> values). What is the role of omitting the NA? Because I tried that both ways and I still get the same plot</p></li>
  <li><p>I can only add the equations as a text which means to run the lm function and then add the relathionship manually in the plot. I need to do that automatically.</p></li>
  </ol>
  
  <p>The code that I am using is:</p>
  
  <pre><code>ggplot(df1, aes(x=noxppb, y=OX, colour = "red")) +
    geom_point(colour = "red", shape=2) +    # Use hollow circles
    geom_smooth(method=lm, se = FALSE) + 
    geom_point(data = df1, aes(x=noxppb, y=OX)) +
    geom_point(colour = "blue", shape=3) +
    geom_smooth(method = lm, se = F, colour = "blue", data = df2, aes(x=noxppb, y=OX)) +
    geom_point(colour = "green", shape=4) +
    geom_smooth(method = lm, se = F, colour = "green", data = df3, aes(x=noxppb, y=OX))
  </code></pre>
  
  <p>I get the following image: <a href="https://i.stack.imgur.com/AznFw.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/AznFw.png" alt="enter image description here"></a></p>
  
  <p>However I Need something similar to this: <a href="https://i.stack.imgur.com/bn1nq.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/bn1nq.jpg" alt="enter image description here"></a></p>