How to use geom_bar and use two categorical variables on the x axis

Question

I try to do a bar plot, with an X axis a bit different than usual. The idea is to represent this axis by the initial variable (code) and by a grouping variable (region). Each code has one region attributed to it. And I would like vertical line to delimitate my regions on the plot.

Here is a reprex

library(dplyr)
library(ggplot2)
data <- tibble::tribble(
                           ~code,    ~term,          ~estimate,           ~std.error,       ~statistic,             ~p.value,      ~region,
                          "ANTA", "t_chla", 0.0577051712200805, 0.000720537559840254, 80.0862778518777, 1.51491004165028e-36,      "Polar",
                          "ARCH", "t_chla", 0.0528096415790542,  0.00237431411186973, 22.2420619559337, 9.38778083531695e-08, "Equatorial",
                          "ARCT", "t_chla", 0.0381489725623347, 0.000549351930679462, 69.4435942277484,  7.1661522966813e-84,      "Polar",
                          "BPLR", "t_chla", 0.0334314725309052, 0.000908084662707285, 36.8153696498248,   6.728272457306e-26,      "Polar",
                          "EMED", "t_chla",  0.048713647973686,  0.00179735526256328, 27.1029601038437, 1.37127584382531e-20,  "Temperate",
                          "SANT", "t_chla", 0.0311278181792805, 0.000594175450783383, 52.3882602996143, 4.93281235468381e-67,      "Polar",
                          "SPSG", "t_chla", 0.0676467149977894,  0.00461643829029263,  14.653442923744, 1.64755108560374e-06, "Equatorial",
                          "WMED", "t_chla", 0.0359293074812375, 0.000954627809780489, 37.6369796826883, 1.88418982949485e-42,  "Temperate"
                          )

data$code <- factor(data$code, levels = c("ANTA", "SANT", "ARCT", "BPLR", "EMED", "WMED", "SPSG", "ARCH"))


ggplot(data)+
  geom_bar(aes(y = estimate, x = code, fill = code), stat = "identity")+
  geom_errorbar(aes(ymin = estimate - std.error, ymax = estimate + std.error, x = code))+
  scale_fill_brewer(palette = "Set1", guide = "none")+
  theme_bw()+
  ylab("Specifc absorption")+
  xlab("Oceanic province")+
  ggtitle("Specific absorption")

So the idea is to have a vertical line between BPLR and EMED and between WMED and SPSG, with the bar grouped under the label Polar, Temperate and Equatorial.

Thanks in advance for your answers.

nniloc · Accepted Answer · 2021-11-23T17:30:30.613

What about adding facet_wrap and panel.spacing = unit(0, 'lines') to your plot?

ggplot(data)+
  geom_bar(aes(y = estimate, x = code, fill = code), stat = "identity")+
  geom_errorbar(aes(ymin = estimate - std.error, ymax = estimate + std.error, x = code))+
  scale_fill_brewer(palette = "Set1", guide = "none")+
  theme_bw()+
  ylab("Specifc absorption")+
  xlab("Oceanic province")+
  ggtitle("Specific absorption") +
  facet_wrap(~region, scales = 'free_x') +
  theme(panel.spacing = unit(0, 'lines'))

Edit: updated to manually add vertical line and labels

Here is another option for adding the grouping to the bars. Lots of customization can be done with text size, position, color, font, etc.

ggplot(data)+
  geom_bar(aes(y = estimate, x = code, fill = code), stat = "identity")+
  geom_errorbar(aes(ymin = estimate - std.error, ymax = estimate + std.error, x = code))+
  scale_fill_brewer(palette = "Set1", guide = "none")+
  theme_bw()+
  ylab("Specifc absorption")+
  xlab("Oceanic province")+
  ggtitle("Specific absorption") +
  geom_vline(xintercept = c(4.5, 6.5)) +
  annotate(geom = 'text', x = 2.5, y = .07, label = 'Polar') +
  annotate(geom = 'text', x = 5.5, y = .07, label = 'Temperate') +
  annotate(geom = 'text', x = 8, y = .07, label = 'Equitorial')

Yes that was my back up solution, I wanted to try something different. But I feel it is not possible using ggplot2. Thanks for your answer. — Flavien PETIT, Nov 22 '21 at 08:24
Edited to add another option where I manually added vertical lines and labels. — nniloc, Nov 22 '21 at 19:46
That is great thanks ! Didn't know we could use xintercept = c(4.5) to that matter ! — Flavien PETIT, Nov 23 '21 at 13:35

How to use geom_bar and use two categorical variables on the x axis

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