如何在条形图中绘制垂直线？

Question

I want to draw a vertical line at specific positions of the x-axis, but the x-positions of the lines aren't correct. How can I solve this ?

x <- c(0,0,0,4,5,6)
barplot(x, names.arg=1:length(x))
abline(v=1:length(x), col="red")
abline(v=c(5.5), col="blue")

Answer 1

You have to save the result of barplot . Then use those values to plot the vertical lines.

x <- c(0,0,0,4,5,6)
bp <- barplot(x, names.arg = seq_along(x))
abline(v = bp, col = "red")
abline(v = 5.5, col = "blue")

Note that the blue line was plotted twice and therefore became violet. So remove the value 5.5 from the first call to `abline

bp <- barplot(x, names.arg = seq_along(x))
abline(v = bp[bp != 5.5], col = "red")
abline(v = 5.5, col = "blue")

Answer 2

If you don't have to stick to base plot , you can do the same using ggplot2 and geom_vline function:

library(ggplot2)
x <- c(0,0,0,4,5,6)
d <- data.frame(x)
ggplot(d, aes(x = seq(1:6), y = x))+
  geom_bar(stat = "identity")+
  scale_x_continuous(breaks = 1:6)+
  geom_vline(xintercept = 1:6, color = "red")+
  geom_vline(xintercept = 5.5, color = "blue")