为同一 ggplot 中使用的不同 data.frames 手动添加额外的图例

Question

In my plot below, I have two separate sources of data ( dat and dat2 ) used in two different geom_smooth() calls producing the black and the red regression lines ( see pic below ).

Is it possible to manually add another legend that shows the black line is called "Between" and red line is called "Within" ?

library(tidyverse)

dat <- read.csv('https://raw.githubusercontent.com/rnorouzian/e/master/cw2.csv')
dat$groups <- factor(dat$groups)

dat2 <- dat %>% group_by(groups) %>% summarize(mean_x = mean(x),
                                               mean_y = mean(y),
                                               .groups = 'drop')
dat %>% 
  ggplot() +
  aes(x, y, color = groups, shape = groups)+
  geom_point(size = 2) + theme_classic()+ 
  stat_ellipse(level = .6) +
  geom_point(data = dat2, 
             mapping = aes(x = mean_x, y = mean_y,fill = factor(groups)),
             size = 4, show.legend = F,shape=21) +
  geom_smooth(data = dat2, mapping = aes(x = mean_x, y = mean_y,group=1), 
          method = "lm", se=F, color = 1, formula = 'y ~ x')+ 
  geom_smooth(aes(group = 1), 
              method = "lm", se=F, color = 2, formula = 'y ~ x')+
  scale_fill_manual(values=rep('black',3))

Answer 1

It looks like you need a second color scale to do this. You can use the ggnewscale package:

library(ggnewscale)

dat %>% 
  ggplot() +
  aes(x, y, color = groups, shape = groups) +
  geom_point(size = 2) + 
  theme_classic() + 
  stat_ellipse(level = .6) +
  geom_point(data = dat2, 
             mapping = aes(x = mean_x, y = mean_y),
             size = 4, show.legend = FALSE, shape = 21, fill = "black") +
  scale_color_discrete() +
  new_scale_color() +
  geom_smooth(data = dat2, 
              mapping = aes(x = mean_x, y = mean_y, group = 1, color = "black"), 
          method = "lm", se = FALSE, formula = 'y ~ x') + 
  geom_smooth(aes(group = 1, color = "red"), 
              method = "lm", se = FALSE, formula = 'y ~ x') +
  scale_color_identity(name = "", labels = c("Between", "Within"),
                       guide = guide_legend())