CODEWITHSUNDEEP
rggplot2legendsubscript
Jellz
Jellz

Reputation: 455

Subscript in multiple legends in ggplot2

To make my figure suitable for black-white printing, I mapped one variable with "shape", "lty", "color" together.

ggplot(df, aes(x=time, y=mean, 
               shape=quality, 
               lty=quality,
               color=quality))

I got the figure like, enter image description here I would like to make part of legends as subscribs, with the codes:

labels=c(expression(Pol[(Art)]), expression(Pol['(Aca-)']), expression(Pol['(Aca-)']))

Unfortunately, when I put the "label" in color or shape, it makes the legend quite complex, like,

enter image description here

Is it possible to map "shape", "color","lty" to one varible, and set the subscript, but keep them in one set of legend?

Upvotes: 6

Views: 3434

Answers (1)

Brian
Brian

Reputation: 8275

To change the labels of a categorical scale, you use scale_*_discrete(labels = ...). Here you just need to do that for color, shape, and linetype.

You should avoid using lty = generally; that synonym is permitted for compatibility with base R, but it's not universally supported throughout ggplot2.

I changed your labels to be closer to what I think you meant (the third entry is now "Aca+" instead of a repeat of "Aca-") and to make them left-align better (by adding an invisible "+" to the first one to create the appropriate spacing).

lab1 <- c(expression(Pol[(Art)*phantom("+")]),
          expression(Pol['(Aca-)']), 
          expression(Pol['(Aca+)']))

library(ggplot2)

ggplot(mtcars, 
       aes(wt, mpg, 
           color = factor(cyl), 
           shape = factor(cyl), 
           linetype = factor(cyl))) +
  geom_point() +
  stat_smooth(se = F) +
  scale_color_discrete(labels = lab1) +
  scale_shape_discrete(labels = lab1) +
  scale_linetype_discrete(labels = lab1)

enter image description here

If you find yourself needing to repeat exact copies of a function like this, there's two workarounds:

  1. Relabel the data itself - OR -

  2. Use purrr::invoke_map to iterate over the functions

library(purrr)

ggplot(mtcars, 
       aes(wt, mpg, 
           color = factor(cyl), 
           shape = factor(cyl), 
           linetype = factor(cyl))) +
  geom_point() +
  stat_smooth(se = F) +
  invoke_map(list(scale_color_discrete, 
                  scale_linetype_discrete, 
                  scale_shape_discrete),
             labels = lab1)

Update:

This approach is mostly fine, but now the expression(...) syntax has a superior alternative, the excellent markdown-based {ggtext} package: https://github.com/wilkelab/ggtext

To change to this method, use a (optionally, named) vector of labels that look like this:

library(ggtext)

lab1 <- c(
  `4` = "Pol<sub>(Art)</sub>",
  `6` = "Pol<sub>(Aca-)</sub>", 
  `8` = "Pol<sub>(Aca+)</sub>"
)

And then add this line to your theme:

  ... +
  theme(
    legend..text = element_markdown()
  )

The advantages over the other method are that:

  1. markdown syntax is a lot easier to search for help online and
  2. now those labels can be stored in the actual data as a column, rather than passing them separately to each geom

You can use that new column as your aesthetic mapping [ggplot(..., aes(color = my_new_column, linetype = my_new_column, ...)] instead of having to pass extra labels in each layer using the purrr::invoke method.

Upvotes: 7

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