R ggplot绘图折线未按预期连接问题求助

问题原因 #

原代码中geom_line的分组设置为interaction(vacc_cover, shape)，相当于把数据拆分为4个独立分组：Slow-Observed、Slow-Interpolated、Rapid-Observed、Rapid-Interpolated，每个分组仅包含1-2个数据点，因此只能生成零散的短线条，无法实现同个插值类型的线条首尾相连。

修正方案 #

根据你的需求，推荐两种实现方式：

方式1：用线型区分插值类型，点颜色区分观测/插值（视觉清晰度最高） #

library(tidyverse)

p2_plt_data <- tibble(year = c(1985, 1990, 1995, 2000, 1985, 1990, 1995, 2000), 
                     p2   = c(0, 0.00127, 0.0641, 0.85, 0, 0.765, 0.850, 0.85),
                     shape = rep(c("Slow", "Rapid"), each = 4),
                     vacc_cover = rep(c("Observed", "Interpolated","Interpolated", "Observed"), times = 2)  
                     )

ggplot(p2_plt_data, aes(x = year, y = p2)) +
  # 仅按shape分组，保证同类型插值的线条完整连接，用线型区分Slow/Rapid
  geom_line(aes(group = shape, linetype = shape), size = 0.8) +
  # 点填充色区分Observed/Interpolated
  geom_point(aes(fill = vacc_cover), shape = 21, size = 2) +
  # 可自定义配色匹配你原有的蓝橙效果
  scale_fill_manual(values = c("Observed" = "#0072B2", "Interpolated" = "#E69F00"))

方式2：线段和点都用颜色区分观测/插值，用点形状区分插值类型 #

如果需要保留线段按Observed/Interpolated分色的需求，可通过geom_segment实现：

library(tidyverse)

p2_plt_data <- tibble(year = c(1985, 1990, 1995, 2000, 1985, 1990, 1995, 2000), 
                     p2   = c(0, 0.00127, 0.0641, 0.85, 0, 0.765, 0.850, 0.85),
                     shape = rep(c("Slow", "Rapid"), each = 4),
                     vacc_cover = rep(c("Observed", "Interpolated","Interpolated", "Observed"), times = 2)  
                     ) %>%
  group_by(shape) %>%
  # 生成下一个点的坐标，用于绘制连续线段
  mutate(next_year = lead(year),
         next_p2 = lead(p2)) %>%
  ungroup()

ggplot(p2_plt_data, aes(x = year, y = p2)) +
  # 线段按shape分组保证连续，颜色对应vacc_cover属性
  geom_segment(aes(xend = next_year, yend = next_p2, colour = vacc_cover, group = shape), size = 0.8, na.rm = T) +
  # 点同时映射颜色和形状，同时区分两类属性
  geom_point(aes(colour = vacc_cover, shape = shape), size = 2) +
  scale_colour_manual(values = c("Observed" = "#0072B2", "Interpolated" = "#E69F00"))

内容的提问来源于stack exchange，提问作者gokhale