geom_bar + geom_line: with different y-axis scale? - r

Question

Is there any way to plot geom_bar with geom_line like the following chart.
I have come up with the two separate charts. How to combine them with two different axes on the left and right sides respectively.
library(ggplot2)
temp = data.frame(Product=as.factor(c("A","B","C")),
N = c(17100,17533,6756),
n = c(5,13,11),
rate = c(0.0003,0.0007,0.0016),
labels = c(".03%",".07%",".16%"))
p1 = ggplot(data = temp, aes(x=Product,y=N))+
geom_bar(stat="identity",fill="#F8766D")+geom_text(aes(label=n,col="red",vjust=-0.5))+
theme(legend.position="none",axis.title.y=element_blank(),axis.text.x = element_text(angle = 90, hjust = 1))
p1
p2 = ggplot(data = temp,aes(x=Product,y=rate))+
geom_line(aes(group=1))+geom_text(aes(label=labels,col="red",vjust=0))+
theme(legend.position="none",axis.title.y=element_blank(),
axis.text.x = element_text(angle = 90, hjust = 0))+
xlab("Product")
p2
Thanks a lot.

Answer 1

Now that ggplot2 has added support for secondary axes (as of version 2.2.0), it is possible to create a graph like this with much less code, within a single ggplot() call (no stacking multiple plots as a workaround!)
ggplot(data = temp, aes(x = Product, y = N)) + #start plot by by plotting bars
geom_bar(stat = "identity") +
#plot line on same graph
# rate multiplied by 10000000 to get on same scale as bars
geom_line(data = temp, aes(x = Product, y = (rate)*10000000, group = 1),
inherit.aes = FALSE) +
#specify secondary axis
#apply inverse of above transformation to correctly scale secondary axis (/10000000)
scale_y_continuous(sec.axis = sec_axis(~./10000000, name = "rate"))
I know this is an older question that has an answer, but wanted to provide an update - due to package updates there is an simpler solution than the one in the accepted answer (which was the best solution at the time).

Answer 2

I'm borrowing most of the code from here:
library(ggplot2)
library(gtable)
library(grid)
temp = data.frame(Product=as.factor(c("A","B","C")),
N = c(17100,17533,6756),
n = c(5,13,11),
rate = c(0.0003,0.0007,0.0016),
labels = c(".03%",".07%",".16%"))
p1 = ggplot(data = temp, aes(x=Product,y=N))+
geom_bar(stat="identity",fill="#F8766D") +
geom_text(aes(label=n,col="red",vjust=-0.5))+
theme(legend.position="none",axis.title.y=element_blank(),
axis.text.x = element_text(angle = 90, hjust = 1))
p2 = ggplot(data = temp,aes(x=Product,y=rate))+
geom_line(aes(group=1))+geom_text(aes(label=labels,vjust=0))+
theme(legend.position="none",axis.title.y=element_blank(),
axis.text.x = element_text(angle = 90, hjust = 0),
panel.background = element_rect(fill = NA),
panel.grid = element_blank())+
xlab("Product")
g1 <- ggplot_gtable(ggplot_build(p1))
g2 <- ggplot_gtable(ggplot_build(p2))
# overlap the panel of 2nd plot on that of 1st plot
pp <- c(subset(g1$layout, name == "panel", se = t:r))
g <- gtable_add_grob(g1, g2$grobs[[which(g2$layout$name == "panel")]], pp$t,
pp$l, pp$b, pp$l)
# axis tweaks
ia <- which(g2$layout$name == "axis-l")
ga <- g2$grobs[[ia]]
ax <- ga$children[[2]]
ax$widths <- rev(ax$widths)
ax$grobs <- rev(ax$grobs)
ax$grobs[[1]]$x <- ax$grobs[[1]]$x - unit(1, "npc") + unit(0.15, "cm")
g <- gtable_add_cols(g, g2$widths[g2$layout[ia, ]$l], length(g$widths) - 1)
g <- gtable_add_grob(g, ax, pp$t, length(g$widths) - 1, pp$b)
# draw it
grid.draw(g)
I removed the grid from the second plot (it appears on top and looks messy).