title: ggplot grouping in x axis
body: <p>I' would like to replicate this chart, 
  <a href="https://i.stack.imgur.com/zR3NM.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/zR3NM.png" alt="enter image description here"></a></p>
  
  <p>though with minimum wages in EUR and PPS. The grouping applies to values in EUR. Everything works fine, but I don't get it how to add the "group" additionally on x axis.
   here my code</p>
  
  <pre><code>library(eurostat)
  library(tidyverse)
  library(ggplot2)
  dat_MW &lt;- get_eurostat(id="earn_mw_cur", time_format="num")
  dat_MW &lt;- label_eurostat(dat_MW)
  dat_MW_w &lt;- dat_MW  %&gt;% filter(time==2017, currency %in% c("Euro","Purchasing Power Standard")) %&gt;% arrange(currency, values)
  dat_MW_w$geo[dat_MW_w$geo=="Germany (until 1990 former territory of the FRG)"] &lt;- "Germany"
  dat_MW_w$geo[dat_MW_w$geo=="Former Yugoslav Republic of Macedonia, the"] &lt;- "Macedonia"
  dat_MW_w$currency[dat_MW_w$currency=="Purchasing Power Standard"] &lt;- "PPS"
  dat_MW_w$currency[dat_MW_w$currency=="Euro"] &lt;- "EUR"
  dat_MW_w &lt;- dat_MW_w %&gt;% 
          mutate(group=ifelse(values&lt;=500 &amp; currency=="EUR","GROUP1", 
                              ifelse(values&lt;=1000 &amp; currency=="EUR", "GROUP2", 
                                     ifelse(currency=="EUR","GROUP3", NA))))
  figure1 &lt;- ggplot(data=dat_MW_w, aes(x=reorder(geo, values), y=values, group=currency)) +
          xlab("Countries") + ylab("EUR/PPS") +
          #ggtitle("Monthy minium wages, in EUR/PPS, 2017 S1") +
          geom_bar(aes(fill=currency),stat = "identity", position = position_dodge()) + 
          theme_minimal() + 
          scale_fill_manual(values=c("#999999", "#E69F00"))+
          theme(axis.text.x = element_text(angle = 90, hjust = 1))
  figure1
  </code></pre>
  
  <p>I appreciate your help :)</p>