Creating legend in R when using ggplot(), geom_smooth

Question

I have created a plot of smooth lined curves of some data along with the corresponding data points with the following code in rstudio:

#begin code
library(ggplot2)
ggplot(mydata, aes(x,y)) + geom_point() + geom_smooth()
p <- ggplot() +

# blue plot
geom_point(data=mydata, aes(x,y)) +
geom_smooth(data=mydata, aes(x,y),fill="blue",
colour ="darkblue", size=1) +

# red plot
geom_point(data=mydata, aes(x,y2)) +
geom_smooth(data=mydata, aes(x,y2), fill="darkred",
colour="red", size=1)

p + xlab('Density') + ylab("Potential Energy (MeV)") 

#endcode

Where data is fed in as x,y,y2 in three columns.

I can get the graphs to work just find, but I cannot figure out how to add a legend. The native legend() function does not work and any attempt to use theme() or scale_colour_manual() just returns the graphs unaltered. How can I add a legend or graphic to differentiate the red and blue curves?

You are not using ggplot in the way that it is intended. Scales should be added automatically if you shape your data correctly. You can then use scale_color_blah to change the scales. Try something along these lines. You need to create a new data.frame that stacks the two columns of y's on top of each other, then create an indicator (`var` in this case) for y and y2. `mydata = data.frame(x = c(mydata$x, mydata$x), y = c(mydata$y, mydata$2), var = c(rep(0, LENGTH OF Y), rep(1, LENGTH of Y2))); ggplot(data = iris, aes(x = x, y = y, color = var)) + geom_point() + geom_smooth()` — Vlo, Sep 08 '16 at 18:21

score 1 · Answer 1 · answered Sep 08 '16 at 18:31

This is the data I used as an example.

   mydata=data.frame(x=seq(1,10),
                  y1=floor(runif(min = 1,max=10,10)),
                  y2=floor(runif(min = 1,max=10,10)))

To have it work with ggplot2 I used the function melt from the reshape2 library.

 mydata=melt(mydata,measure.vars = c("y1","y2"))

I then used the following code, lmk if that fits your need:

ggplot(mydata,aes(x,value))+
  geom_point(aes(fill=as.factor(variable)))+
  geom_smooth(aes(fill=as.factor(variable)))+
  scale_fill_manual(values=c("red","blue"),guide=guide_legend(title="Variable"))

Creating legend in R when using ggplot(), geom_smooth

1 Answers1