R: How to add a label on the right axis in a ggplot barchart?-CodePudding

Suppose I create a ggplot barplot with this code:

mtcars$carb<-as.character(mtcars$carb)
mtcars$gear<-as.character(mtcars$gear)
mtcars$carb_labelright<-paste0("label_right",mtcars$carb)

#pelacolset
ggplot(mtcars, 
       #color by which to fill
       aes(fill=gear, 
           #y axis
           y=wt, 
           #x axis
           x=carb))  
  #title and subtitle
  
  
  #barplot
  geom_bar(position="fill", stat="identity",width=.8) 
  coord_flip() 
  

  #rotate x axis labels 90 degrees
  theme(axis.text.x = element_text(angle=90),
        panel.grid.major = element_blank(),
        panel.grid.minor = element_blank(),
        panel.border = element_blank(),
        panel.background = element_blank())

The plot looks like this:

Now I would like to use the column carb_labelright to add the data on the right side of the bar plot. It should look like this:

How can this be done?

CodePudding user response：

I find easiest to annotate with geom_text (you'll need a data frame) or with annotate(geom = "text",...). Using annotate is usually safer, as geom_text likes to create a label for each row (which is fine when you use carefully prepared data frames for annotation).

library(tidyverse)
mtcars$carb<-as.character(mtcars$carb)
mtcars$gear<-as.character(mtcars$gear)
mtcars$carb_labelright<-paste0("label_right",mtcars$carb)

ggplot(mtcars)  
  # use geom_col, a convenience wrapper for geom_bar(stat = "identity")
  geom_col(aes(fill=gear, y=wt, x=carb), 
           position="fill", width=.8)  
  # you have to turn clipping off
  coord_flip(clip = "off")  
  annotate(geom = "text", x = unique(mtcars$carb),
           label = unique(mtcars$carb_labelright),
           y = 1, hjust = 0)  
  # you need to increase the legend's margin and make it "transparent"
  # otherwise you will cover some labels. 
  theme(legend.margin = margin(l = 1, unit = "inch"),
        legend.background = element_blank())

^{Created on 2021-10-26 by the reprex package (v2.0.1)}

CodePudding user response：

I also ran into the problem of discrete axes not supporting secondary scales (see related issue on the ggplot2 repo). I solved it by writing a manual guide myself that does allow me to make secondary axes with discrete scales. In the code below, we use ggh4x::guide_axis_manual() in combination with an rlang/purrr lambda function to format the labels. (Disclaimer: I'm the author of ggh4x).

library(ggplot2)
#> Warning: package 'ggplot2' was built under R version 4.1.1

mtcars$carb<-as.character(mtcars$carb)
mtcars$gear<-as.character(mtcars$gear)
mtcars$carb_labelright<-paste0("label_right",mtcars$carb)

p <- ggplot(mtcars, 
       aes(fill = gear, y = carb, x = wt))  
  geom_col(position="fill", width=.8)

p   guides(
  y.sec = ggh4x::guide_axis_manual(
    labels = ~ paste0("label_right_", .x)
  )
)

Alternatively, you can give the labels as a character vector directly too.

p   guides(
  y.sec = ggh4x::guide_axis_manual(
    labels = sort(unique(mtcars$carb_labelright))
  )
)

^{Created on 2021-10-26 by the reprex package (v2.0.1)}