r - 如何将带有新数据的图层添加到带有 POSIX 轴的 ggplot 中？

Question

如果我想向 ggplot 添加一个点，我已经习惯了这个，它工作得很好:

ggplot(mtcars, aes(x = disp, y = mpg)) + geom_point() +
    geom_point(x = 200, y = 20, size = 5, color = "blue")

但是，如果涉及 POSIX 日期，我会遇到问题:

dat_1 <- data.frame(time = as.POSIXct(c("2010-01-01", "2010-02-01", "2010-03-01")),
                     y_1 = c(-1, 0, 1))

当然，基本情节是可行的

(my_plot <- ggplot(dat_1, aes(x = time, y = y_1)) +
    geom_point())

但又加了一层

my_plot + geom_point(x = as.POSIXct("2010-01-01"),
    y = 0, size = 5, color = "blue")

返回错误

Error in Ops.POSIXt((x - from[1]), diff(from)) : 
  '/' not defined for "POSIXt" objects

Answer 1

转换为数字解决了这个问题:

my_plot + geom_point(x = as.numeric(as.POSIXct("2010-01-01")),
    y = 0, size = 5, color = "blue")

但如果映射在aes 包装器中则没有必要

point_data <- data.frame(x = as.POSIXct("2010-01-01"), y = 0)
my_plot + geom_point(aes(x = x, y = y), data = point_data,
                     size = 5, color = "blue"