ggplot：使用分面图上方的单独数据添加注释

Question

我正在尝试在多面图表顶部上方添加一组带有文本的标记，以指示 x 值中的某些兴趣点。重要的是它们出现在从左到右的正确位置（根据主要比例），包括当整体 ggplot 改变大小时。

这样的……

但是，我正在努力：

• 将其放置在正确的垂直位置（小平面上方）。在我的 下面的reprex（原始版本的简化版本），我尝试使用 因子的值（Merc450 SLC），但这会导致诸如将其添加到 每个方面，包括当它不是该方面的一部分并且不属于该方面时 实际上足够高。我还尝试使用 as.integer 将因子转换为数字，但这会导致每个方面都包含所有因子值，而它们显然不应该
• 应用于整个图表，而不是每个 方面

请注意，在完整解决方案中，标记 x 值与主要数据无关。

我曾尝试使用 cowplot 单独绘制并覆盖它，但这似乎是： 影响主情节的整体规模，右侧的刻面标题被裁剪 将标记放置在沿 x 刻度的确切位置是不可靠的

欢迎指点。

library(tidyverse)
                
mtcars2 <- rownames_to_column(mtcars, var = "car") %>%
  mutate(make = stringr::word(car, 1)) %>%
  filter(make >= "m" & make < "n")
markers <- data.frame(x = c(max(mtcars2$mpg), rep(runif(nrow(mtcars2), 1, max(mtcars2$mpg))), max(mtcars2$mpg))) %>%
  mutate(name = paste0("marker @ ", round(x)))


ggplot(mtcars2, aes()) +
  # Main Plot
  geom_tile(aes(x = mpg, y = car, fill = cyl), color = "white") +
  # Add Markers
  geom_point(data = markers, aes(x = x, y = "Merc450 SLC"), color = "red") +
  # Marker Labels
  geom_text(data = markers, aes(x = x, "Merc450 SLC",label = name), angle = 45, size = 2.5, hjust=0, nudge_x = -0.02, nudge_y = 0.15) +
  facet_grid(make ~ ., scales = "free", space = "free") +
  theme_minimal() +
  theme(
    # Facets
    strip.background = element_rect(fill="Gray90", color = "white"),
    panel.background = element_rect(fill="Gray95", color = "white"),
    panel.spacing.y = unit(.7, "lines"),
    plot.margin = margin(50, 20, 20, 20)
  )

Answer 1

也许画两个单独的图，用patchwork组合在一起：

library(patchwork) 

p1 <- ggplot(markers, aes(x = x,  y = 0)) +
    geom_point(color = 'red') +
    geom_text(aes(label = name),
        angle = 45, size = 2.5, hjust=0, nudge_x = -0.02, nudge_y = 0.02) +
    scale_y_continuous(limits = c(-0.01, 0.15), expand = c(0, 0)) +
    theme_minimal() +
    theme(axis.text = element_blank(),
        axis.title = element_blank(),
        panel.grid = element_blank())

p2 <- ggplot(mtcars2, aes(x = mpg, y = car, fill = cyl)) +
    geom_tile(color = "white") +
    facet_grid(make ~ ., scales = "free", space = "free") +
    theme_minimal() +
    theme(
        strip.background = element_rect(fill="Gray90", color = "white"),
        panel.background = element_rect(fill="Gray95", color = "white"),
        panel.spacing.y = unit(.7, "lines")
    )

p1/p2 + plot_layout(heights = c(1, 9))

Answer 2

它需要一些解决方法，在不同的绘图上绘制绘图并使用cowplot 对齐功能将它们对齐在同一轴上。这是一个解决方案

library(tidyverse)
library(cowplot)

# define a common x_axis to ensure that the plot are on same scales
# This may not needed as cowplot algin_plots also adjust the scale however
# I tended to do this extra step to ensure.
x_axis_common <- c(min(mtcars2$mpg, markers$x) * .8,
  max(mtcars2$mpg, markers$x) * 1.1)

# Plot contain only marker
plot_marker <- ggplot() +
  geom_point(data = markers, aes(x = x, y = 0), color = "red") +
  # Marker Labels
  geom_text(data = markers, aes(x = x, y = 0,label = name),
    angle = 45, size = 2.5, hjust=0, nudge_x = 0, nudge_y = 0.001) +
  # using coord_cartesian to set the zone of plot for some scales
  coord_cartesian(xlim = x_axis_common,
    ylim = c(-0.005, 0.03), expand = FALSE) +
  # using theme_nothing from cow_plot which remove all element
  # except the drawing
  theme_nothing()

# main plot with facet
main_plot <- ggplot(mtcars2, aes()) +
  # Main Plot
  geom_tile(aes(x = mpg, y = car, fill = cyl), color = "white") +
  coord_cartesian(xlim = x_axis_common, expand = FALSE) +
  # Add Markers
  facet_grid(make ~ ., scales = "free_y", space = "free") +
  theme_minimal() +
  theme(
    # Facets
    strip.background = element_rect(fill="Gray90", color = "white"),
    panel.background = element_rect(fill="Gray95", color = "white"),
    panel.spacing.y = unit(.7, "lines"),
    plot.margin = margin(0, 20, 20, 20)
  )

然后对齐绘图并使用cow_plot绘制它们

# align the plots together
temp <- align_plots(plot_marker, main_plot, axis = "rl",
  align = "hv")

# plot them with plot_grid also from cowplot - using rel_heights for some
# adjustment
plot_grid(temp[[1]], temp[[2]], ncol = 1, rel_heights = c(1, 8))

^{由reprex package (v2.0.0) 于 2021 年 5 月 3 日创建}