Changing axis ticks labels to months names and expressions in `geom_bar`

Question

I am trying to customize a plot for this data.

x <- 1:12
z1 <- c("m", "m", "m", "m", "m", "n", "n", "n", "n", "n", "n", "n")
z2 <- c("m", "m", "m", "m", "p", "p", "p", "p", "n", "n", "n", "n")
z3 <- c("m", "m", "m", "p", "p", "p", "n", "n", "n", "n", "n", "n")

So I created a data frame and plotted it.

df <- data.frame(x, z1, z2, z3)
colors <- c("m" = "#f8766d", "n" = "#00BA38", "p" = "#619CFF")

df_long <- pivot_longer(df, cols = c("z1", "z2", "z3"), names_to = "variable", values_to = "value")

df_long$value <- factor(df_long$value, levels = c("m", "n", "p"))

ggplot(df_long, aes(x = variable, fill = value)) +
  geom_bar(position = position_stack(reverse = TRUE)) +
  coord_flip()

The output is not bad; it looks like this.

But we would like to have three ticks on the x-axis as Jan, Feb, Mar. So Jan would be where x=1, then Feb would be where x=5and Mar would be where x=9.

On the y-axis, we would like to have z(t,1), z(t,2), z(t,3) but in italic like what we do with expression() in labels.

Is it possible to do these? Could someone help please?

Answer 1

Starting from your plot object p you can change and customize tick marks and labels.

As you mentioned Jan is placed where x=1 (1 occurrence of m, n or p ,Feb is placed at 5 occurrence)

p=ggplot(df_long, aes(x = variable, fill = value)) +
  geom_bar(position = position_stack(reverse = TRUE)) +
  coord_flip()
p +  theme(axis.text.y = element_text(face="italic")) +
    scale_x_discrete(breaks=c("z1","z2","z3"),
                      labels=c("z(t,1)", "z(t,2)", "z(t,3)"))+
    scale_y_continuous(breaks=c(1,5,9),
                     labels=c("Jan", "Feb", "Mar")) 

^{Created on 2023-04-03 with reprex v2.0.2}