title: Adding a point to the ggplot messes up the legend
body: <p>I have a data dataframe </p>
  
  <pre><code>dat &lt;- data.frame(cond = rep(c("A", "B"), each=10),
                    xvar = 1:20 + rnorm(20,sd=3),
                    yvar = 1:20 + rnorm(20,sd=3))
  </code></pre>
  
  <p>I want to scatter-plot it using <code>ggplot2</code></p>
  
  <p>Lets say the additional point would just be <code>15th</code> row in the data</p>
  
  <pre><code>g1 &lt;- dat[15,]
  </code></pre>
  
  <p>I can now generate the plot<a href="https://i.stack.imgur.com/4IDup.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/4IDup.png" alt="enter image description here"></a></p>
  
  <p>using </p>
  
  <pre><code>scat1 &lt;- ggplot(dat, aes(x=dat[,2], y=dat[,3], shape=factor(dat[,1]), size=2.5, 
       colour = factor(dat[,1]))) + geom_point(alpha=1)
  #Add point to the plot 
  scat1 &lt;- scat1 + geom_point(x=g1[,2],y=g1[,3], 
  colour="blue", size=4)   # this adds a blue point 
  #here the legend goes awry and color changes to blue
  #Add a label for the added point 
  scat1 &lt;- scat1 + geom_text(x=g1[,2], y=1+g1[,3], label="Added", col="Black") 
  # this adds a label for the blue point
  # Format the figure 
  scat1 &lt;- scat1 + theme(panel.grid.major = element_blank(),
           panel.grid.minor = element_blank(), 
           axis.text=element_text(size=14), 
           plot.title = element_text(size = rel(2), 
           colour = "black", face="bold"),
           axis.title=element_text(size=16,face="bold"),
           panel.background = element_blank(), 
           axis.line = element_line(colour = "black"),
           legend.text=element_text(size=14), 
           axis.text.x = element_blank(),
           legend.title=element_text(size=14),
           legend.justification = c(1, 1), 
           legend.position = c(0.25,1))
  #Add sensible xlabel and ylabel 
  scat1 &lt;- scat1 + ylab(colnames(dat)[3]) +  xlab(colnames(dat)[2]) 
  scat1 &lt;- scat1 + ggtitle(paste("The variable", colnames(dat)[2], "and", colnames(dat)[3] )) 
  #Delete multiple legends and add a suitable title to the legend
  scat1 &lt;- scat1 + guides(shape=guide_legend(title="sale year"), size=FALSE, 
            color= guide_legend(title="sale year")) 
  </code></pre>
  
  <p>However, I want to change the legend to shape and color matching the original color and shape in the image like the one shown below. How can I do that?
  <a href="https://i.stack.imgur.com/wcY2r.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/wcY2r.png" alt="enter image description here"></a></p>