使用ggplot重现折线图时生成Race分类变量失败如何解决？

• 你的代码第一个问题出在case_when的判断条件中使用了&&运算符：&&是标量逻辑与，仅返回单个逻辑值，无法对数据集逐行判断，需要替换为支持逐行运算的矢量化&运算符。
• 第二个问题是不需要对数据按type和shortcut分组，直接在全量数据集上执行mutate即可生成race分类变量。

修正后完整代码 #

# 生成race分类变量
newdata <- records %>%
  mutate(race = case_when( 
    type == "Three lap" & shortcut == "No" ~ "Three lap with no shortcut",
    type == "Three lap" & shortcut == "Yes" ~ "Three lap with shortcut",
    type == "Single lap" & shortcut == "No" ~ "Single lap with no shortcut",
    type == "Single lap" & shortcut == "Yes" ~ "Single lap with shortcut"
  )) 

# 绘制目标可视化图
ggplot(data = newdata, mapping = aes(x = date, y = time, color = race)) +
  geom_line() + 
  geom_point()

如果需要调整图例的展示顺序，可以手动指定race的因子水平：

newdata$race <- factor(newdata$race, 
                       levels = c("Three lap with no shortcut", 
                                  "Three lap with shortcut",
                                  "Single lap with no shortcut",
                                  "Single lap with shortcut"))

内容的提问来源于stack exchange，提问作者Thuy Nguyen