ggplot绘制直方图加均值标准差线时报object未找到错误如何解决

错误原因 #

你遇到的报错核心原因是：ggplot 图层中未写在aes()内的参数，不会自动从你指定的west数据框中查找变量。你在geom_vline的xintercept参数中直接写mean(NoHealthInsurance)时，R会默认从全局环境搜索NoHealthInsurance对象，找不到就会抛出对应错误。

解决方法 #

可以选择以下任意一种方案修改代码：

方案1：直接指定变量所属数据框 #

在所有用到NoHealthInsurance的位置增加数据框前缀west$即可，修改后代码如下：

hist <- ggplot(data = west) +
  geom_histogram(aes(NoHealthInsurance), 
                 color = wes_palette("Zissou1", 1), 
                 fill = wes_palette("Zissou1", 2)[2]) +
  geom_vline(xintercept = mean(west$NoHealthInsurance)) +
  geom_vline(xintercept = mean(west$NoHealthInsurance) - sd(west$NoHealthInsurance), color = "blue") +
  geom_vline(xintercept = mean(west$NoHealthInsurance) + sd(west$NoHealthInsurance), color = "blue") +
  geom_vline(xintercept = mean(west$NoHealthInsurance) - 2*sd(west$NoHealthInsurance), color = "red", linetype = "dotted") +
  geom_vline(xintercept = mean(west$NoHealthInsurance) + 2*sd(west$NoHealthInsurance), color = "red", linetype = "dotted")

方案2：提前计算统计量（更推荐，代码更整洁易维护） #

先将均值、标准差提前计算存储为变量，再传入绘图参数，避免重复计算：

# 提前计算均值和标准差
mu <- mean(west$NoHealthInsurance)
sigma <- sd(west$NoHealthInsurance)

hist <- ggplot(data = west) +
  geom_histogram(aes(NoHealthInsurance), 
                 color = wes_palette("Zissou1", 1), 
                 fill = wes_palette("Zissou1", 2)[2]) +
  geom_vline(xintercept = mu) +
  geom_vline(xintercept = mu - sigma, color = "blue") +
  geom_vline(xintercept = mu + sigma, color = "blue") +
  geom_vline(xintercept = mu - 2*sigma, color = "red", linetype = "dotted") +
  geom_vline(xintercept = mu + 2*sigma, color = "red", linetype = "dotted")

内容的提问来源于stack exchange，提问作者Naurica