如何使用 ggplot2 在直线和倒置 geom_density() 之间添加垂直空白空间

Question

I am trying to reproduce this kind of Figure, with two densities, a first one pointing upwards and a second one pointing downwards. I would also like to have some blank space between the two densities.

Here is the code I am currently using.

library(hrbrthemes)
library(tidyverse)
library(RWiener)

# generating data
df <- rwiener(n = 1e2, alpha = 2, tau = 0.3, beta = 0.5, delta = 0.5)

df %>%
  ggplot(aes(x = q) ) +        
  geom_density(
    data = . %>% filter(resp == "upper"),
    aes(y = ..density..),
    colour = "steelblue", fill = "steelblue",
    outline.type = "upper", alpha = 0.8, adjust = 1, trim = TRUE
    ) +
  geom_density(
    data = . %>% filter(resp == "lower"),
    aes(y = -..density..), colour = "orangered", fill = "orangered",
    outline.type = "upper", alpha = 0.8, adjust = 1, trim = TRUE
    ) +
  # stimulus onset
  geom_vline(xintercept = 0, lty = 1, col = "grey") +
  annotate(
    geom = "text",
    x = 0, y = 0,
    # hjust = 0,
    vjust = -1,
    size = 3, angle = 90,
    label = "stimulus onset"
    ) +
  # aesthetics
  theme_ipsum_rc(base_size = 12) +
  theme(axis.text.y = element_blank() ) +
  labs(x = "Reaction time (in seconds)", y = "") +
  xlim(0, NA)

Which results in something like...

How could I add some vertical space between the two densities to reproduce the above Figure?

Answer 1

If you want to try without faceting, you're probably best to just plot the densities as polygons with adjusted y values according to your desired spacing:

s <- 0.25 # set to change size of the space

ud <- density(df$q[df$resp == "upper"])
ld <- density(df$q[df$resp == "lower"])
x <- c(ud$x[1], ud$x, ud$x[length(ud$x)], 
       ld$x[1], ld$x, ld$x[length(ld$x)])
y <- c(s, ud$y + s, s, -s, -ld$y - s, -s)
df2 <- data.frame(x = x, y = y, 
                  resp = rep(c("upper", "lower"), each =  length(ud$x) + 2))

df2 %>%
  ggplot(aes(x = x, y = y, fill = resp, color = resp) ) +
  geom_polygon(alpha = 0.8) +
  scale_fill_manual(values = c("steelblue", "orangered")) +
  scale_color_manual(values = c("steelblue", "orangered"), guide = guide_none()) +
  geom_vline(xintercept = 0, lty = 1, col = "grey") +
  annotate(
    geom = "text",
    x = 0, y = 0,
    # hjust = 0,
    vjust = -1,
    size = 3, angle = 90,
    label = "stimulus onset"
    ) +
  # aesthetics
  theme_ipsum_rc(base_size = 12) +
  theme(axis.text.y = element_blank() ) +
  labs(x = "Reaction time (in seconds)", y = "")

Answer 2

you can try facetting

set.seed(123)
q=rbeta(100, 0.25, 1)

df_dens =data.frame(gr=1,
                    x=density(df$q)$x,
                    y=density(df$q)$y)

df_dens <- rbind(df_dens,
      data.frame(gr=2,
                 x=density(df$q)$x,
                 y=-density(df$q)$y))



ggplot(df_dens, aes(x, y, fill = factor(gr))) + 
   scale_x_continuous(limits = c(0,1)) +
   geom_area(show.legend = F) + 
   facet_wrap(~gr, nrow = 2, scales = "free_y") + 
   theme_minimal() +
   theme(strip.background = element_blank(),
        strip.text.x = element_blank(),
        axis.text.y = element_blank(),
        axis.title.y = element_blank())

The space between both plots can be increased using panel.spacing = unit(20, "mm") . Instead of facet_grid you can also try facet_grid(gr~., scales = "free_y")