Strip label customization in facet_wrap

Question

I want to shift the strip label of the facet graph in Col-2 to the right side. As i marked in the graph,

I am using this code

library(reshape2)
library(tidyverse)
library(ggh4x)
library(scales)
library(ggplot2)
#step 1: mutate the data
df <- melt(df, id=c("Specie","Treatment"))
head(df)
#plotting
left  <- scale_y_continuous(labels = number_format(accuracy = 0.01))
right <- scale_y_continuous(labels = number_format(accuracy = 0.01),position = "right")

ggplot(df1, aes(x = Specie, y = mean, fill = Treatment, colour=Treatment)) +
  geom_col(position = position_dodge(), width = 0.8)+
  facet_wrap(~ variable, scales = "free_y", ncol = 2, 
             labeller = label_parsed, strip.position = "left")+
  geom_errorbar(aes(ymin = mean, ymax = mean + sd), width = 0.2,
                position = position_dodge(0.9)) +theme_bw()+
  geom_text(aes(y = mean+sd,label = label),position = position_dodge(0.9),
            size = 3.5, vjust=-0.2, family="serif", colour="black")+
  geom_text(aes(y = Q1/2,label = letter),size = 3.5, family="serif", colour="#000000")+
  scale_fill_manual(values=c('#DEB887','#CD853F'))+
  scale_color_manual(values=c('#DEB887','#CD853F'))+
  facetted_pos_scales(y = list(left, right, left, right, left, right))+
  #coord_flip()+
  theme(axis.text.x = element_text(face = "italic"),
        strip.placement = "outside",
        strip.background = element_blank())

Here is the example dataset

Treatment	Specie	Pn	Gs	E	WUE
CT	S. commersonii	4.8100	0.0736	1.1100	4.3333
CT	S. commersonii	11.5000	0.4660	5.4400	2.1140
CT	S. tuberosum 2x	16.4000	0.4930	5.5200	2.9710
CT	S. tuberosum 2x	4.2400	0.0862	1.8100	2.3425
CT	S. chacoense	3.9200	0.0426	0.7160	5.4749
CT	S. chacoense	7.9000	0.1500	1.9400	4.0722
HS	S. commersonii	10.1000	0.3520	6.0300	1.6750
HS	S. commersonii	6.8500	0.3700	5.4600	1.2546
HS	S. tuberosum 2x	4.7100	0.0205	0.8400	5.6071
HS	S. tuberosum 2x	4.3400	0.0314	1.2450	3.4859
HS	S. chacoense	13.8000	0.2450	6.4800	2.1296
HS	S. chacoense	14.4000	0.1700	5.5100	2.6134

Answer 1

You could use the patchwork package and piece together two plots, making the labels be individual then patched together with a shared axis/legend. This doesn't include all the specifications in your plot (e.g., error bars, colors, text), but the general idea is:

library(patchwork)


#Creating dataset and adding grouping variable
mod_iris <- iris %>% 
    group_by(Species) %>% 
    mutate(average_petal_length = mean(Petal.Length)) %>% 
    mutate(species_length_group = case_when(Petal.Length <= average_petal_length ~ "Short",
                                            TRUE ~ "Long")) %>% 
    select(-average_petal_length) %>% 
    ungroup() %>% 
    pivot_longer(cols = "Sepal.Length":"Petal.Width")  

#Create two datasets

#One for length

iris_lengths_data <- mod_iris %>% 
    filter(!str_detect(name,"Width"))

#This will be plot that has information on the left
length_plot <- iris_lengths_data %>% 
    ggplot(aes(x = Species, y = value, fill = species_length_group, color = species_length_group)) +
    geom_bar(stat = "identity", position = "dodge") +
    facet_wrap(.~name, scales = "free_y", ncol = 1, strip.position = "left") +
    theme(strip.placement = "outside")



#One for width

iris_widths_data <- mod_iris %>% 
    filter(str_detect(name,"Width"))
    
#This will be plot that has information on the right
width_plot <- iris_widths_data %>% 
    ggplot(aes(x = Species, y = value, fill = species_length_group, color = species_length_group)) +
    geom_bar(stat = "identity", position = "dodge") +
    facet_wrap(.~name, scales = "free_y", ncol = 1, strip.position = "right") +
    scale_y_continuous(position = "right") +
    labs(y = NULL)+ #Removed to have just one y axis
    theme(strip.placement = "outside",
          strip.text.y.right = element_text(angle = 90))  #adjusted to have text in same direction as length plot

    

#Patch together 
iris_patch <- length_plot + width_plot + plot_layout(guides = "collect") & xlab(NULL) & theme(legend.position = "right")


#Add common x-axis and position
wrap_elements(panel = iris_patch) +
    labs(tag = "Species") +
    theme(plot.tag = element_text(size = rel(1)),
          plot.tag.position = c(.415, 0))