根据是否满足条件对绘图区域进行着色

我正在使用创建线图ggplot() and geom_line()随着时间的推移而发展的价值观走廊。

有时可能会发生上限低于下限（我将其称为“反转”），并且我想突出显示在我的图中发生这种情况的区域，例如使用不同的背景颜色。

搜索 Google 和 StackOverflow 都没有给我带来任何结果。

这是一个人为的例子：

library(tidyverse)
library(RcppRoll)

set.seed(42)
N <- 100
l <- 5
a <- rgamma(n = N, shape = 2)
d <- tibble(x = 1:N, upper = roll_maxr(a, n = l), lower = roll_minr(a + lag(a), n = l)) %>% mutate(inversion = upper < lower)
dl <- pivot_longer(d, cols = c("upper", "lower"), names_to = "Bounds", values_to = "bound_vals")

ggplot(dl, mapping = aes(x = x, y = bound_vals, color = Bounds)) + geom_line(linewidth = 1) + theme_light()

这会产生以下图：

正如您所看到的，反转发生在一些地方，例如大约x = 50。我希望情节有一个较暗的（比如灰色）背景，基于inversion列已经在标题中。我怎样才能做到这一点？

非常感谢你的帮助！

实现您想要的结果的一种选择是使用ggh4x::stat_difference像这样。请注意，为此我们必须使用宽数据集并相应地通过两个添加行geom_line.

library(ggplot2)
library(ggh4x)

ggplot(d, mapping = aes(x = x)) + 
  stat_difference(aes(ymin = lower, ymax = upper)) +
  geom_line(aes(y = lower, color = "lower"), linewidth = 1) + 
  geom_line(aes(y = upper, color = "upper"), linewidth = 1) + 
  scale_fill_manual(values = c("+" = "transparent", "-" = "darkgrey"),
                    breaks = "-",
                    labels = "Inversion") +
  theme_light() +
  labs(color = "Bounds")

EDIT当然，也可以为交叉区域绘制背景矩形。但我不知道有任何现成的选项，即棘手的部分是计算线相交处的 x 值，这需要一些努力和近似。这是一种方法，但可能不是最有效的方法。

library(tidyverse)

# Compute intersection points and prepare data to draw rects
n <- 20 # Increase for a better approximation 
rect <- data.frame(
  x = seq(1, N, length.out = N * n)
)

# Shamefully stolen from ggh4x
rle_id <- function(x) with(rle(x), rep.int(seq_along(values), lengths))

rect <- rect |> 
  mutate(lower = approx(d$x, d$lower, x)[["y"]],
         upper = approx(d$x, d$upper, x)[["y"]],
         inversion = upper < lower,
         rle = with(rle(inversion & !is.na(inversion)), rep.int(seq_along(values), lengths))
        ) |>
  filter(inversion) |> 
  group_by(rle) |> 
  slice(c(1, n())) |>
  mutate(label = c("xmin", "xmax")) |> 
  ungroup() |> 
  select(x, rle, label) |> 
  pivot_wider(names_from = label, values_from = x)


ggplot(dl, mapping = aes(x = x, y = bound_vals, color = Bounds)) + 
  geom_line(linewidth = 1) + 
  geom_rect(data = rect, aes(xmin = xmin, xmax = xmax, group = rle), 
            ymin = -Inf, ymax = Inf, fill = "darkgrey", alpha = .3, inherit.aes = FALSE) +
  theme_light()
#> Warning: Removed 9 rows containing missing values (`geom_line()`).