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rggplot2

Creating a plot with the average values across the variable levels

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

enter image description here

Solution

  • Not 100% sure about your desired result. If you want to create the same chart without differentiating by Group, then drop color=Group and use group = 1 in the stat_summary which draws the line to connect the means:

    library(ggplot2)
library(dplyr, warn = FALSE)

set.seed(123)

interaction_plot <- df %>%
  mutate(frequency = factor(frequency, levels = c("Alpha", "Beta", "Theta"))) %>%
  ggplot(aes(x = task, y = power)) +
  stat_summary(
    fun = mean, geom = "line", aes(group = 1), 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