如何使用R中的ggplot将单点添加到多线图中？

install.packages("ggplot2")

library(ggplot2)

df <- data.frame(x = c(1, 2, 3, 4, 5),
                 y1 = c(2, 4, 6, 8, 10),
                 y2 = c(3, 6, 9, 12, 15),
                 y3 = c(4, 8, 12, 16, 20))

p <- ggplot(data = df, aes(x = x, y = y1))

p <- p + geom_line(aes(y = y2))
p <- p + geom_line(aes(y = y3))

p <- p + geom_point(data = df[df$x == 3, ], aes(y = y3))

library(ggplot2)

df <- data.frame(x = c(1, 2, 3, 4, 5),
                 y1 = c(2, 4, 6, 8, 10),
                 y2 = c(3, 6, 9, 12, 15),
                 y3 = c(4, 8, 12, 16, 20))

p <- ggplot(data = df, aes(x = x, y = y1))
p <- p + geom_line(aes(y = y2))
p <- p + geom_line(aes(y = y3))
p <- p + geom_point(data = df[df$x == 3, ], aes(y = y3))

# 可以根据需要进行美化
# p <- p + scale_color_manual(values = c("red", "blue", "green"))
# p <- p + scale_shape_manual(values = c(16, 17, 18))

print(p)