ggplot2 - add subscript after label in bar

Question

I am trying to add a label (noun) after another label (number) in a bar chart (example below). It works well with normal text (creating a column like Value2 in the example), but if I need a subscript, It doesn't work.

I tried some workarounds with "bquote" and "expression" but didn't figure it out. The idea is to have the numbers in the GHG variable appearing as a subscript in the Figure (CO[2], CH[4] and N[2]O).

Any insights? Simple working example below

GHG = c("CH4", "CO2", "N2O")

Value = c(10, 5, 2)

Value2 = c("10 - CH4", "5 - CO2", "2 - N2O")

df = data.frame(GHG, Value, Value2)

g1 = ggplot(data=df, aes(x=GHG, y=Value)) +
  
  geom_bar(stat="identity") +
  
  geom_text(data=df, aes(label = Value2, y= Value, hjust=-0.1), size=4) +
        
  xlab ("") +
  ylab ("") +
  
  coord_flip() +
  
  scale_y_continuous(limits=c(0,11)) + 
  
  theme(text=element_text(family="serif", size=15, colour="black")) +
  theme(axis.text.x=element_text(size=15, colour = "black")) +
  
  easy_remove_y_axis() 

g1

Answer 1

One way would be to use ggtext package where you can use <sub> and <sup> tags.

library(ggplot2)
library(ggtext)
library(ggeasy)

GHG = c("CH4", "CO2", "N2O")
Value = c(10, 5, 2)
Value2 = c("10 - CH<sub>4</sub>", "5 - CO<sub>2</sub>", "2 - N<sub>2</sub>O")
df = data.frame(GHG, Value, Value2)

ggplot(data=df, aes(x=GHG, y=Value)) +
  geom_col() +
  geom_richtext(aes(label = Value2, hjust=-0.1), size=4) +
  xlab ("") +
  ylab ("") +
  coord_flip() +
  scale_y_continuous(limits=c(0,11)) + 
  theme(text=element_text(family="serif", size=15, colour="black")) +
  theme(axis.text.x=element_text(size=15, colour = "black")) + 
  easy_remove_y_axis()