allowing duplicate x axis categorical groups in ggplot2::geom_bar

library(ggplot2)
library(viridis)
library(hrbrthemes)

# create a dataset
specie <- c(rep("sorgho" , 3) , rep("poacee" , 3) , rep("banana" , 3) , rep("triticum" , 3) )
condition <- rep(c("normal" , "stress" , "Nitrogen") , 4)
value <- abs(rnorm(12 , 0 , 15))
data <- data.frame(specie,condition,value, stringsAsFactors = FALSE)
data$condition[c(11, 12)] <- "other"

# Graph
ggplot(data, aes(fill = condition, y=value, x=condition)) + 
  geom_bar(position="dodge", stat="identity") +
  scale_fill_viridis(discrete = T, option = "E") +
  ggtitle("Studying 4 species..") +
  facet_grid(specie~., scales = "free", space = "free") +
  theme_ipsum() +
  theme(legend.position="none") +
  xlab("") +
  coord_flip() +
  theme(strip.text.x = element_text(angle = 0)) +
  theme_classic()

There are 2 rows in the triticum facet that contain the value other for the column condition.

This is done so that 2 separate bars will appear for this value. Instead, only 1 bar appears. How can the former be accomplished?

Solution

One option could be to define a helper variable for the plot, say cond2, in data with discrete names, but label by condition using scale_x_discrete, e.g.:

library(ggplot2)
library(viridis)
specie <- c(rep("sorgho" , 3) , rep("poacee" , 3) , rep("banana" , 3) , rep("triticum" , 3) )
condition <- rep(c("normal" , "stress" , "Nitrogen") , 4)
value <- abs(rnorm(12 , 0 , 15))
data <- data.frame(specie,condition,value, stringsAsFactors = FALSE)
data$condition[c(11, 12)] <- "other"
data$cond2 <- data$condition
data$cond2[c(11, 12)] <- make.unique(data$condition[c(11, 12)]) 

# Graph
ggplot(data, aes(fill = condition, y=value, x=cond2)) + 
    geom_bar(position="dodge", stat="identity") +
    scale_fill_viridis(discrete = T, option = "E") +
    scale_x_discrete(labels=setNames(data$condition, data$cond2)) +
    ggtitle("Studying 4 species..") +
    facet_grid(specie~., scales = "free", space = "free") +
    theme(legend.position="none") +
    xlab("") +
    coord_flip() +
    theme(strip.text.x = element_text(angle = 0)) +
    theme_classic()

^{Created on 2021-05-31 by the reprex package (v2.0.0)}