R：将自定义图例添加到 ggplot

Question

我有以下情节：

并想添加如下图例：

这是我用来生成绘图的代码：

library(data.table)
library(ggplot2)

blue <- "#4472C4"
green <- "#548235"
red <- "#C55A11"
redblood <- "#C00000"

DT <- data.table(student = c("Jane", "Sam", "Tim", "Kate", "Claire"),
                 grade = c(10, 14, 8, 9, 19))

b0 <- 13

DT[, gradeHat := b0]
DT[, e := grade - gradeHat]
DT[, SS := sum(e**2)]

DT[, id := 1:nrow(DT)]
DT[, xmin := id]
DT[, xmax := id + abs(e)/20*3]
DT[, ymin := min(grade, gradeHat), id]
DT[, ymax := max(grade, gradeHat), id]
DT[, student := factor(student, levels = student)]

gg <- ggplot(DT) +
  geom_segment(aes(x = student, xend = student, y = grade, yend = gradeHat),
               color = redblood, size = 1.3) +
  geom_rect(aes(xmin = xmin, xmax = xmax, ymin = ymin, ymax = ymax),
            fill = redblood, alpha = .4) +
  geom_hline(yintercept = b0, color = green, alpha = .7, size = 1, linetype = "dashed") +
  geom_point(aes(student, grade), color = blue, size = 4) +
  geom_point(aes(student, gradeHat), color = green, size = 4) +
  scale_y_continuous(breaks = 0:20, limits = c(0, 20)) +
  coord_fixed(.15) +
  theme_classic()

plot(gg)

Answer 1

不是您问题的完整解决方案......但我目前能想到的最好的解决方案：

1. 要在 ggplot 中获得图例，您必须在美学上进行映射，即，您必须映射到 color 或 aes() 内的 color 或 fill 上，而不是将颜色设置为参数。为此，您可以使用占位符或标签，例如fill="SS" 在geom_rect。

2. 要获得正确的颜色，您可以使用scale_color/fill_manual。使用标签可以很容易地分配正确的颜色。

3. 接下来，要正确设置图例的样式，您可以使用guide_legend 及其参数override.aes 来设置颜色图例的形状和线型。

4. 默认情况下，color 和 fill 图例之间有一些间距，但可以通过 legend.spacing 和 legend.margin 在 theme() 中删除。

5. 最后一部分是给图例标签上色。这可以通过ggtext 包实现，该包通过主题选项legend.text = element_markdown() 允许使用HTML 和CSS 设置图例条目的样式。

很遗憾，我无法弄清楚如何在您的 gradeHat 上戴上宽帽。

library(data.table)
library(ggplot2)

blue <- "#4472C4"
green <- "#548235"
red <- "#C55A11"
redblood <- "#C00000"

DT <- data.table(student = c("Jane", "Sam", "Tim", "Kate", "Claire"),
                 grade = c(10, 14, 8, 9, 19))

b0 <- 13

DT[, gradeHat := b0]
DT[, e := grade - gradeHat]
DT[, SS := sum(e**2)]

DT[, id := 1:nrow(DT)]
DT[, xmin := id]
DT[, xmax := id + abs(e)/20*3]
DT[, ymin := min(grade, gradeHat), id]
DT[, ymax := max(grade, gradeHat), id]
DT[, student := factor(student, levels = student)]

ggplot(DT) +
  geom_segment(aes(x = student, xend = student, y = grade, yend = gradeHat, color = "error"),
               , size = 1.3) +
  geom_rect(aes(xmin = xmin, xmax = xmax, ymin = ymin, ymax = ymax, fill = "SS"), alpha = .4) +
  geom_hline(yintercept = b0, color = green, alpha = .7, size = 1, linetype = "dashed") +
  geom_point(aes(student, grade, color = "grade"), size = 4) +
  geom_point(aes(student, gradeHat, color = "gradeHat"), size = 4) +
  scale_color_manual(breaks = c("grade", "gradeHat", "error"), 
                     values = c(grade = blue, gradeHat = green, error = red),
                     labels = c(grade = glue::glue("<span style = 'color: {blue};'>grade</span>"),
                                gradeHat = glue::glue("<span style = 'color: {green};'>gradeHat</span>"), 
                                error = glue::glue("<span style = 'color: {red};'>error</span>"))) +
  scale_fill_manual(values = c(SS = redblood), labels = c(SS = glue::glue("<span style = 'color: #C0000066; '>SS</span>"))) +
  guides(color = guide_legend(order = 1, override.aes = list(shape = c(16, 16, NA), linetype = c("blank", "dashed", "solid")))) +
  scale_y_continuous(breaks = 0:20, limits = c(0, 20)) +
  coord_fixed(.15) +
  theme_classic() +
  theme(legend.position = "bottom", 
        legend.spacing = unit(0, "pt"), 
        legend.margin = margin(r = 0, l = 0),
        legend.text = ggtext::element_markdown()) +
  labs(color = NULL, fill = NULL)

Answer 2

是的，这（几乎）是可能的：

gg <- ggplot(DT) +
  geom_segment(aes(x = student, xend = student, y = grade, yend = gradeHat,
               color = "Error"), size = 1.3) +
  geom_rect(aes(xmin = xmin, xmax = xmax, ymin = ymin, ymax = ymax, fill = "SS"),
            alpha = .4) +
  geom_hline(aes(alpha = "Grade", yintercept = 13), linetype = 2,
             color = green, size = 1, key_glyph = "pointrange") +
  geom_point(aes(student, grade, shape = "Grade"), color = blue, size = 4) +
  geom_point(aes(student, gradeHat), color = green, size = 4)  +
  scale_y_continuous(breaks = 0:20, limits = c(0, 20)) +
  scale_shape_manual(values = 19, name = NULL, guide = guide_legend(order = 1)) +
  scale_color_manual(values = redblood, name = NULL, 
                     guide = guide_legend(order = 3)) +
  scale_alpha_manual(breaks = "Grade", values = 1,
                    guide = guide_legend(order = 2,
                                         override.aes = list(color = green)),
                    name = "") +
  scale_fill_manual(values = redblood, name = NULL) +
  coord_fixed(.15) +
  theme_classic() +
  theme(legend.position = "bottom",
        legend.key.width = unit(20, "points")) 

plot(gg)