如何为ggplot2散点图中指定站点的图形添加黑色轮廓？

初始实现 #

我用ggplot2绘制散点图，通过形状和颜色区分不同站点（Site），初始代码及效果如下：

all <- ggplot(data = all_quantity, aes(x=Distance, y=Quantity, shape=Site, colour=Site)) +
  geom_point(size=3) + # 设置点大小
  scale_y_continuous(limits = c(0, 80), breaks = c(0, 10, 20, 30, 40, 50, 60, 70, 80)) + # Y轴刻度
  scale_x_continuous(limits = c(0, 30), breaks = c(0, 5, 10, 15, 20, 25, 30)) + # X轴刻度
  labs(y="Quantity (pg/mL)", x="Downstream Distance (km)")
all

需求与问题 #

我希望给Belton、Bridgeport、Canyon这三个站点的点添加黑色轮廓，避免颜色混杂难以区分。尝试了以下代码：

all <- ggplot(data = all_quantity, aes(x=Distance, y=Quantity, shape=Site, fill=Site)) +
  geom_point(size=3, colour="black") +
  scale_shape_manual(values = c(21, 24, 22, 3, 7, 8)) +
  scale_y_continuous(limits = c(0, 80), breaks = c(0, 10, 20, 30, 40, 50, 60, 70, 80)) + # Y轴刻度
  scale_x_continuous(limits = c(0, 30), breaks = c(0, 5, 10, 15, 20, 25, 30)) + # X轴刻度
  labs(y="Quantity (pg/mL)", x="Downstream Distance (km)")
all

这段代码实现了目标站点的黑色轮廓，但Lewisville、Stillhouse、Worth三个站点的颜色变成了黑色，无法保留初始图中的原有颜色。

解决方案 #

核心思路是区分带填充的形状（如21、24、22，支持fill和colour分别设置填充色与轮廓色）和无填充的形状（如3、7、8，仅受colour控制），针对两类站点分别设置颜色参数：

# 定义站点对应的形状与颜色（颜色匹配初始ggplot默认配色）
site_shapes <- c(
  "Belton" = 21, "Bridgeport" = 24, "Canyon" = 22,
  "Lewisville" = 3, "Stillhouse" = 7, "Worth" = 8
)
site_colors <- c(
  "Belton" = "#F8766D", "Bridgeport" = "#00BA38", "Canyon" = "#619CFF",
  "Lewisville" = "#F8766D", "Stillhouse" = "#00BA38", "Worth" = "#619CFF"
)

all <- ggplot(data = all_quantity, aes(x=Distance, y=Quantity)) +
  # 针对不同站点设置填充、轮廓和形状
  geom_point(size=3,
             aes(
               shape = Site,
               # 目标站点用黑色轮廓，其他站点用自身颜色
               colour = ifelse(Site %in% c("Belton", "Bridgeport", "Canyon"), "black", Site),
               # 目标站点设置填充色，其他站点无需填充
               fill = ifelse(Site %in% c("Belton", "Bridgeport", "Canyon"), Site, NA)
             )) +
  # 手动指定形状、颜色和填充
  scale_shape_manual(values = site_shapes) +
  scale_colour_manual(values = c("black" = "black", site_colors)) +
  scale_fill_manual(values = site_colors, guide = "none") +
  # 保留原有的轴设置和标签
  scale_y_continuous(limits = c(0, 80), breaks = c(0, 10, 20, 30, 40, 50, 60, 70, 80)) +
  scale_x_continuous(limits = c(0, 30), breaks = c(0, 5, 10, 15, 20, 25, 30)) +
  labs(y="Quantity (pg/mL)", x="Downstream Distance (km)", shape="Site")
all

说明 #

1. 带填充的形状（21、24、22）会显示填充色（fill）+黑色轮廓（colour），完美实现目标站点的效果；
2. 无填充的形状（3、7、8）仅受colour控制，直接使用站点原有颜色，和初始图保持一致；
3. 通过scale_colour_manual和scale_fill_manual统一颜色，确保配色和初始图匹配。

内容的提问来源于stack exchange，提问作者Coral Rivell