Based on the example below, I want to create the same chart using the average values of “power” over hemisphere (left and right) and region (frontal and motor).

More specifically, I would like two columns in the chart: hemisphere (based on the average value over left and right) and region (based on the average value over frontal and motor).

I appreciate any suggestions!

library(ggplot2)  
library(dplyr)  

df <- expand.grid(  
  group = c("Children", "Teenagers"),  
  task = c("A", "B", "C"),  
  hemisphere = c("Left", "Right"),  
  region = c("Frontal", "Motor"),  
  frequency = c("Alpha", "Beta", "Theta")  
)  

df$power <- runif(nrow(df))  
print(df)  


interaction_plot <- df %>%   
  mutate(frequency = factor(frequency, levels = c("Alpha", "Beta", "Theta"))) %>%  
  ggplot(aes(x = task, y = power, color = group)) +  
  stat_summary(fun = mean, geom = "line", aes(group = group), size = 1.5) +  
  stat_summary(fun.data = mean_cl_boot, geom = "errorbar", width = 0.3, position = position_dodge(0.2)) +  
  facet_grid(frequency ~ hemisphere + region, space = "free_y", scales = "free_y") +  
  labs(title = "",  
       x = "Task", y = "Mean EEG Band Power",  
       color = "Group") +  
  theme_minimal(base_size = 12) +  
  theme(strip.background = element_blank(),  # Optional: remove strip background for clarity  
        strip.text.y = element_text(angle = 0, hjust = 0.5, size = 14))  # Adjust text angle and size  

interaction_plot