QCC's xbar chart recreated in ggplot2

create_xbar_chart.R

# Load libraries -------
library(ggplot2)
library(dplyr)

# Function to create X-bar chart
create_xbar_chart <- function(
    data, 
    x_var, 
    y_var, 
    title = "" 
    ) {
  
  # Constants
  annot_hjust <- 0.5
  cl_weight <- 0.9
  xbar_color <- "blue"
  cl_color <- "red"
  
  # Capture variable names
  x_var <- enquo(x_var)
  y_var <- enquo(y_var)
  
  # Calculate control limits
  values <- data %>% pull(!!y_var)
  x_bar <- mean(values)
  sigma <- sd(values)
  n <- length(values)
  UCL <- x_bar + 3 * sigma / sqrt(n)
  LCL <- x_bar - 3 * sigma / sqrt(n)
  
  # Create a new column for color coding
  data <- data %>% mutate(status = ifelse(!!y_var > UCL | !!y_var < LCL, "Out of Control", "In Control"))
  
  # Get the minimum x value for annotations
  min_x <- min(data %>% pull(!!x_var))
  max_x <- max(data %>% pull(!!x_var), na.rm = TRUE)
  
  # Create X-bar chart
  ggplot(data) +
    # geom_rect(aes(xmin = min_x, xmax = max_x, ymin = LCL, ymax = UCL), fill = "lightgray", alpha = 0.5) +
    geom_line(aes(x = !!x_var, y = !!y_var), color = "black") +
    geom_hline(yintercept = x_bar, color = xbar_color) +
    geom_hline(yintercept = UCL, linetype = "dashed", color = cl_color, linewidth = cl_weight) +
    geom_hline(yintercept = LCL, linetype = "dashed", color = cl_color, linewidth = cl_weight) +
    geom_point(size = 5, color = "white", aes(x = !!x_var, y = !!y_var)) +
    geom_point(size = 3, aes(x = !!x_var, y = !!y_var, color = status)) +
    annotate("text", x = max_x, y = UCL, label = paste("UCL =", round(UCL, 2)), hjust = annot_hjust, vjust = -0.5, color = "red") +
    annotate("text", x = max_x, y = LCL, label = paste("LCL =", round(LCL, 2)), hjust = annot_hjust, vjust = 1.5, color = "red") +
    annotate("text", x = max_x, y = x_bar, label = paste("CL =", round(x_bar, 2)), hjust = annot_hjust, vjust = -0.5, color = "blue") +
    labs(
      title = paste0("X-Bar Chart: ", title),
      color = "Status"
    ) +
    scale_color_manual(values = c("In Control" = "black", "Out of Control" = "red")) +
    # theme_ipsum_rc() + 
    theme_minimal() + 
    theme(legend.position = "top")
}

# Testing-----------------

## Create dummy dataframe -------
set.seed(123)
example_data <- data.frame(
  date = as.Date('2023-01-01') + 0:24,
  value = rnorm(25, mean = 10, sd = 1)
)

## Create the chart --------
create_xbar_chart(
  data = example_data, 
  x_var = date,
  y_var = value,
  title = "Test Data"
) + 
  labs(
    subtitle = "It is a ggplot2 object, so continue customizing the plot as you normally would!",
    caption = "Peter Yates www.linkedin.com/in/peteryates1 2024.",
    x = "Date",
    y = "Average Daily Measurement"
  )