How to set multiple legends / scales 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 and from vdf
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)

the legend for colour includes only entries from iris, and not from vdf. how can I make ggplot2 add a legend from data=vdf, which in this case would be a gray line below the legend for iris? thanks.

Now you can use `ggnewscale` this will let you add a new scale slot for colour/fill. Here for more information — RobertoSupe, Aug 09 '20 at 02:24

score 7 · Accepted Answer · edited Nov 19 '18 at 12:33

7

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)

enter image description here

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'))

enter image description here

edited Nov 19 '18 at 12:33

tjebo

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answered Jul 14 '13 at 18:18

agstudy

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@agstudy: but I want the line to be gray and also for the legend to be separate. Note that when you do the above, it changes all the legends for the other species to be bold lines, even though the other species are not plotted bold so it looks confusing. Is there a way to get two legends? – Jul 14 '13 at 18:52
3

@user248237dfsf agstudy is correct. **ggplot2** by design will not allow multiple legends for the same aesthetic (i.e. 2 colour legends, 2 fill legends, etc.). – joran Jul 14 '13 at 20:17

tjebo · Answer 2 · 2022-07-11T08:04:08.143

There is currently no vanilla ggplot2 option to set two scales for the same aesthetic.

There are, as of today (July 2022), "only" three packages available to allow creation of more than one scale for the same aesthetic. These are

the relayer package (maintainer Claus Wilke) - not on CRAN
the ggh4x package (on CRAN, maintainer Teun van den Brand)
the ggnewscale package (on CRAN, maintainer Elio Campitelli)

The ggnewscale package comes with three functions, new_scale_color, new_scale_fill, and new_scale for other aesthetics than color or fill.

library(ggplot2)
library(ggnewscale)

vdf <- iris[which(iris$Species == "virginica"), ]

ggplot(iris) +
  geom_line(aes(x = Sepal.Width, y = Sepal.Length, colour = Species)) +
  ## the guide orders are not a necessary part of the code 
  ## this is added for demonstrating purpose and because
  ## the OP wanted a grey line below the Species
  scale_color_discrete(guide = guide_legend(order = 1)) +
  ## add the new scale here
  new_scale_color() +
  ## then add a new color aesthetic, all else as per usual
  geom_line(
    data = vdf, aes(x = Sepal.Width, y = Sepal.Length, colour = "vdf"),
    size = 2
  ) +
  scale_color_manual(NULL, values = "grey", guide = guide_legend(order = 2))

^{Created on 2022-07-03 by the reprex package (v2.0.1)}

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

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