How to set multiple legends for the same aesthetic in ggplot2?

Question

I am plotting data from multiple dataframes in ggplot2 as follows:

# subset of iris data
vdf = iris[which(iris$Species == \"virginica\"),]
# plot from iris a         


        

Answer 1

You should set the color as an aes to show it in the legend.

# subset of iris data
vdf = iris[which(iris$Species == "virginica"),]
# plot from iris and from vdf
library(ggplot2)
ggplot(iris) + geom_line(aes(x=Sepal.Width, y=Sepal.Length, colour=Species)) +
  geom_line(aes(x=Sepal.Width, y=Sepal.Length, colour="gray"), 
            size=2, data=vdf)

EDIT I don't think you can't have a multiple legends for the same aes. here aworkaround :

library(ggplot2)
ggplot(iris) + 
  geom_line(aes(x=Sepal.Width, y=Sepal.Length, colour=Species)) +
  geom_line(aes(x=Sepal.Width, y=Sepal.Length,size=2), colour="gray",  data=vdf) +
   guides(size = guide_legend(title='vdf color'))