For ggplot2 legend key, add border that matches color of other aesthetics with not fill

Question

I am doing a ggplot in which color, fill, shape and linetype aesthetics are used. I would like the legend keys to have no fill, but I would like the color of the legend key border to match the color for the other aesthetics in the legend. Everything in the plot below is as I want it to be except the border.

Please let me know how I can make the color of the border for each key match the color for the rest of the key (i.e. the border for A would be gray, B would be yellow, C would be blue and D would be green).

library(tidyverse)

# Create sample data
set.seed(1)
dat <- data.frame(var_a = rnorm(20), 
                  var_b = rep(c('A', 'B', 'C', 'D'), 5)) %>%
  mutate(response = case_when(var_b == 'A' ~ var_a + 1,
                              var_b == 'B' ~ var_a * 2,
                              var_b == 'C' ~ var_a * .5,
                              var_b == 'D' ~ 1)) %>%
  mutate(response = response + rnorm(nrow(.), 0, 0.1))



# Map colors to values of var_b
custom_color <- c('A' = "#999999", 'B' = "#F0E442", 
                    'C' = "#56B4E9", 'D' = "#009E73")

# Create custom theme
my_theme <- theme_bw() +
  theme(legend.position = 'top',
        legend.key.width = unit(0.35, 'in'))

# Create list with theme and manual aesthetic assignment
my_theme_list <- list(my_theme, 
                      scale_color_manual(values = custom_color),
                      scale_fill_manual(values = custom_color))

# Plot
plot_1 <- dat %>% ggplot(aes(x = var_a, y = response, color = var_b, shape = var_b,
                   linetype = var_b, fill = var_b)) +
  geom_point() +
  geom_smooth(method = 'lm') +
  my_theme_list +
  guides(shape = guide_legend(override.aes = list(fill = NA))) +
  # Here's the part that's not working
  theme(legend.key = element_rect(color = custom_color))

plot_1

# Somehow plot(ggeffect()) is able to color the legend key boxes, but I can't
#  figure out how it does it
library(ggeffect)
mod <- lm(response ~ var_a * var_b, data = dat)

plot(ggeffect(mod, c('var_a', 'var_b'))

i think what you're trying to achieve does not bring any extra information to the plot. the colours are represented as a line inside each legend box already. since colour and fill assume same colour patterns, the legend completely explains the plot. in terms of aesthetics your plot is also looking good (in my opinion).. — rodolfoksveiga
@rodolfoksveiga - I agree, but I am working on a similar plot for someone who does not want to use color in case a plot is copied in black and white. It seems a dated policy, but I'm trying to provide what they requested. Thanks for the comment. — jmar

stefan stefan · Accepted Answer · 2020-11-02T21:51:16

The issue is that via theme you can draw a border around the keys, however to the best of my knowledge you can not have different border colors for the keys. One way to to achieve your desired result is by means of a custom key glyph which combines the default point glyph (draw_key_point) for geom_point with a rectangle glyph (draw_key_rect):

library(tidyverse)

# Create sample data
set.seed(1)
dat <- data.frame(var_a = rnorm(20), 
                  var_b = rep(c('A', 'B', 'C', 'D'), 5)) %>%
  mutate(response = case_when(var_b == 'A' ~ var_a + 1,
                              var_b == 'B' ~ var_a * 2,
                              var_b == 'C' ~ var_a * .5,
                              var_b == 'D' ~ 1)) %>%
  mutate(response = response + rnorm(nrow(.), 0, 0.1))



# Map colors to values of var_b
custom_color <- c('A' = "#999999", 'B' = "#F0E442", 
                  'C' = "#56B4E9", 'D' = "#009E73")

# Create custom theme
my_theme <- theme_bw() +
  theme(legend.position = 'top',
        legend.key.width = unit(0.35, 'in'))

# Create list with theme and manual aesthetic assignment
my_theme_list <- list(my_theme, 
                      scale_color_manual(values = custom_color),
                      scale_fill_manual(values = custom_color))

# Plot
draw_key_cust <- function(data, params, size) {
  grid::grobTree(
    grid::rectGrob(gp = grid::gpar(
      col = data$colour, 
      fill = data$fill, 
      lty = data$linetype)),
    grid::pointsGrob(0.5, 0.5, 
                     pch = data$shape,
                     gp = grid::gpar(
                       col = data$colour,
                       fill = data$fill,
                       fontsize = data$size * .pt))
  )
}

plot_1 <- dat %>% ggplot(aes(x = var_a, y = response, color = var_b, shape = var_b,
                             linetype = var_b, fill = var_b)) +
  geom_point(key_glyph = "cust") +
  geom_smooth(method = 'lm') +
  my_theme_list +
  guides(shape = guide_legend(override.aes = list(fill = NA)))

plot_1
#> `geom_smooth()` using formula 'y ~ x'

For ggplot2 legend key, add border that matches color of other aesthetics with not fill

2 Answers