ggplot修改点颜色/形状时丢失数据致空白图的技术问询

我帮你排查了问题所在，核心原因是手动设置颜色/形状尺度时，没有匹配因子的内部水平值，导致ggplot无法找到对应映射，最终点被判定为缺失值而移除。

问题分析 #

你在代码中已经将year因子的显示标签替换成了长文本，但注意：因子的levels是内部存储的取值（原始的"p"/"c"），labels只是显示用的文本。如果你在设置scale_color_manual或scale_shape_manual时，错误地用长文本作为取值名称，而非原始的"p"/"c"，就会出现匹配失败，所有点变成缺失值，触发警告并显示空白图表。

解决方案 #

方案1：推荐使用原始水平名设置尺度

你的因子转换代码是正确的，只需在颜色/形状尺度中用原始的"p"/"c"作为键名即可：

library(ggplot2)
set.seed(1)
# 创建示例数据
point_est <- 4:1
se <- runif(4)
df <- data.frame(point_est = point_est, se = se, lower = point_est - se, upper = point_est + se, year = c("c", "c", "p", "p"), group = letters[1:4])
group_names <- paste0("Display Name for \n Group ", LETTERS[1:4])
names(group_names) <- letters[1:4]
legend_text <- c("Previous Year Rate with 95% Confidence Intervals", "Current Year Rate with 95% Confidence Intervals")
names(legend_text) <- c("p", "c")
df$year = factor(df$year, levels = names(legend_text), labels = legend_text)
df$group = factor(df$group, levels = names(group_names), labels = group_names)

# 正确设置颜色和形状的代码
ggplot(df, aes(x = group, y = point_est, color = year, shape = year)) + 
  geom_errorbar(aes(ymin=lower, ymax=upper), width=.3) + 
  geom_point(size = 3.2) + 
  scale_x_discrete(drop=FALSE) + 
  scale_y_continuous(sec.axis = sec_axis(~.*3, name = "This is my Right Axis")) + 
  # 用原始水平名"p"/"c"指定颜色和形状
  scale_color_manual(values = c("p" = "#2c3e50", "c" = "#e74c3c")) +
  scale_shape_manual(values = c("p" = 16, "c" = 17)) +
  labs(x = NULL, y = "This is my Left Axis") + 
  theme(legend.title = element_blank())

方案2：用长文本作为尺度名称不推荐，过于繁琐

如果你坚持想用长文本设置尺度，需要完整写出标签内容：

ggplot(df, aes(x = group, y = point_est, color = year, shape = year)) + 
  geom_errorbar(aes(ymin=lower, ymax=upper), width=.3) + 
  geom_point(size = 3.2) + 
  scale_x_discrete(drop=FALSE) + 
  scale_y_continuous(sec.axis = sec_axis(~.*3, name = "This is my Right Axis")) + 
  scale_color_manual(values = c(
    "Previous Year Rate with 95% Confidence Intervals" = "#2c3e50", 
    "Current Year Rate with 95% Confidence Intervals" = "#e74c3c"
  )) +
  scale_shape_manual(values = c(
    "Previous Year Rate with 95% Confidence Intervals" = 16, 
    "Current Year Rate with 95% Confidence Intervals" = 17
  )) +
  labs(x = NULL, y = "This is my Left Axis") + 
  theme(legend.title = element_blank())

额外验证 #

你可以通过以下代码确认因子的内部结构，确保levels是原始的"p"/"c"，labels是长文本：

str(df$year)
# 预期输出： Factor w/ 2 levels "Previous Year Rate...",..: 2 2 1 1

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