Example
Add one common horizontal line for all categorical variables
# sample data
df <- data.frame(x=('A', 'B'), y = c(3, 4))
p1 <- ggplot(df, aes(x=x, y=y))
+ geom_bar(position = "dodge", stat = 'identity')
+ theme_bw()
p1 + geom_hline(aes(yintercept=5), colour="#990000", linetype="dashed")
Add one horizontal line for each categorical variable
# sample data
df <- data.frame(x=('A', 'B'), y = c(3, 4))
# add horizontal levels for drawing lines
df$hval <- df$y + 2
p1 <- ggplot(df, aes(x=x, y=y))
+ geom_bar(position = "dodge", stat = 'identity')
+ theme_bw()
p1 + geom_errorbar(aes(y=hval, ymax=hval, ymin=hval), colour="#990000", width=0.75)
Add horizontal line over grouped bars
# sample data
df <- data.frame(x = rep(c('A', 'B'), times=2),
group = rep(c('G1', 'G2'), each=2),
y = c(3, 4, 5, 6),
hval = c(5, 6, 7, 8))
p1 <- ggplot(df, aes(x=x, y=y, fill=group))
+ geom_bar(position="dodge", stat="identity")
p1 + geom_errorbar(aes(y=hval, ymax=hval, ymin=hval),
colour="#990000",
position = "dodge",
linetype = "dashed")
Add vertical line
# sample data
df <- data.frame(group=rep(c('A', 'B'), each=20),
x = rnorm(40, 5, 2),
y = rnorm(40, 10, 2))
p1 <- ggplot(df, aes(x=x, y=y, colour=group)) + geom_point()
p1 + geom_vline(aes(xintercept=5), color="#990000", linetype="dashed")
