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Shiny Structure

Introduction

This article outlines how I structure my R Shiny codebase. Whenever I start a new Shiny application, I use the following structure:

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modules/
utils/
ui.R
server.R
global.R

Separation of UI Logic and Server Logic

In Mastering Shiny by Hadley Wickham, the ui and server logic are combined in app.R. However, I prefer to separate them into ui.R and server.R for better organization.

Template for server.R

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library(shiny)
library(bs4Dash)

# Define server logic
server <- function(input, output) {
 set.seed(122) 
}

I always set a seed for reproducibility, ensuring consistency in functions that involve pseudo-randomness (e.g., random sampling).

Example of ui.R

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library(shiny)
library(bs4Dash)
library(fresh)

# Sidebar -----------------------------------------------------------------

sidebar <- dashboardSidebar(
  sidebarMenu(
    menuItem("Home", tabName = "home", icon = icon("home"))
  )
)


# Body --------------------------------------------------------------------

body <- dashboardBody(
  fresh::use_theme(theme), # theme is defined in global.R
  tabItems(
    tabItem(
      tabName = "home",
      fluidRow(
      )
    )
  )
)


# Header ------------------------------------------------------------------

header <- dashboardHeader(title = "TOMIC")

# Dashboard Page ----------------------------------------------------------

# Define UI for application
ui <- dashboardPage(
  freshTheme = theme,
  header,
  sidebar,
  body
)

This setup leverages the fresh package for theming alongside bs4Dash.

Global Functions and Variables

The global.R file is automatically recognized by Shiny. It stores global variables and functions used throughout the application. For specific functions, I place them in the utils/ directory.

Template for global.R

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library(fresh)

# Source ------------------------------------------------------------------

## utils
util_file_names <- list.files(path = "utils/", pattern = "\\.R$", full.names = TRUE)
lapply(util_file_names, source)

## modules
mods_file_names <- list.files(path = "modules/", pattern = "\\.R$", full.names = TRUE)
lapply(mods_file_names, source)

This ensures all modules and utility functions are automatically loaded.

Example of global.R

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library(fresh)

# Source ------------------------------------------------------------------

## utils
util_file_names <- list.files(path = "utils/", pattern = "\\.R$", full.names = TRUE)
lapply(util_file_names, source)

## modules
mods_file_names <- list.files(path = "modules/", pattern = "\\.R$", full.names = TRUE)
lapply(mods_file_names, source)

# Theme -------------------------------------------------------------------

# Create the theme
theme <- fresh::create_theme(
  bs4dash_color(
  #   green = "#3fff2d",
  #   blue = "#2635ff",
  #   red = "	#ff2b2b",
  #   yellow = "#feff6e",
  #   fuchsia = "#ff5bf8",
  #   navy = "#374c92",
  #   purple = "#615cbf",
  #   maroon = "#b659c9",
  #   lightblue = "#5691cc"
    lightblue = "#434C5E"
  ),
  bs4dash_sidebar_light(
    bg = "#D8DEE9",
    hover_bg = "#81A1C1",
    color = "#2E3440"
  ),
  bs4dash_sidebar_dark(
    bg = "#2E3440",
    hover_bg = "#81A1C1",
    color = "#D8DEE9"
  ),
  bs4dash_vars(
    content_bg = "#FFF",
    box_bg = "#D8DEE9", 
    info_box_bg = "#D8DEE9"
  )
)

# Global Variables --------------------------------------------------------

watchlist <- c("MARA", "NVDA", "CELH", "BITX", "PL")
markets <- c("^NDX", "^GSPC", "^DJI", "^TNX") # Nasdaq100 and SP500

# Functions ----
get_yearly_data <- function(ticker) {
  data <- tq_get(ticker, get = "stock.prices", complete_cases = TRUE)
  data %>% filter(date >= today() - months(12))
}
get_weekly_data <- function(ticker) {
  data <- tq_get(ticker, get = "stock.prices", complete_cases = TRUE)
  data %>% filter(date >= today() - weeks(1))
}

plot_index_graph <- function(data) {
  ggplotly({
    data %>%
      ggplot(aes(date, close)) +
      geom_line(size = 0.4, alpha = .9) +
      xlab("Time") +
      ylab("Points") +
      theme_minimal()
  })
}

The theme variable is referenced in ui.R to apply consistent styling.

Utilities (utils/)

Example: utils/ticker_utils.R

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symbol_daily_performance <-
  function(ticker,
           sym_name,
           sym_emoji = "",
           value_font_size = "150%") {
    value_font_size <- paste("font-size: ", value_font_size, ";", sep = "")
    sym <-
      tq_get(
        ticker,
        from = lubridate::today() - 7,
        to = lubridate::today() + lubridate::days(1)
      ) %>%
      group_by(symbol) %>%
      slice_tail(n = 2) %>%
      mutate(
        symbol_move = round(close - lag(close, 1), digits = 2),
        symbol_move_return = round(
          (close - lag(close, 1)) / lag(close, 1) * 100,
          digits = 2
        )
      ) %>%
      drop_na(symbol_move) %>%
      select(symbol, date, symbol_move, symbol_move_return)
    sym_subtitle <- paste("+", sym$symbol_move, " (+", sym$symbol_move_return, "%)", sep = "")
    sym_color <- "gray"
    sym_icon <- "ellipsis-horizontal"
    sym_value <- ""
    if (sym$symbol_move_return > 0) {
      sym_color <- "success"
      sym_icon <- "trending-up"
    } else if (sym$symbol_move_return < 0) {
      sym_color <- "danger"
      sym_icon <- "trending-down"
    }
    bs4ValueBox(
      value =
        tags$p(
          paste(sym_name, " ", sym_value, " ", sym_emoji),
          style = value_font_size
        ),
      subtitle = sym_subtitle,
      color = sym_color,
      icon = ionicon(sym_icon)
    )
  }

Modules (modules/)

Shiny modules allow for better reusability and maintainability.

Example: modules\watchlist_mod.R

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watchlistUI <- function(id) {
  ns <- NS(id)
  tagList(
    box(
      title = uiOutput(ns("watchlist_placeholder")),
      id = ns("watchlist"),
      DT::DTOutput(ns("watchlist"))
    )
  )
}

watchlistServer <- function(id, watchlist) {
  moduleServer(
    id,
    function(input, output, session) {
      # watch list
      watchlist_data <-
        tq_get(
          watchlist,
          from = lubridate::today() - 7,
          to = lubridate::today() + lubridate::days(1)
        ) %>%
        group_by(symbol) %>%
        slice_tail(n = 2) %>%
        mutate(
          symbol_move = round(close - lag(close, 1), digits = 2),
          symbol_move_return = round(
            (close - lag(close, 1)) / lag(close, 1) * 100,
            digits = 2
          ),
          close = round(close, digits = 2)
        ) %>%
        drop_na(symbol_move) %>%
        select(symbol, date, symbol_move, symbol_move_return, close)

      output$watchlist_placeholder <- renderUI({
        title <- paste("Watchlist ", watchlist_data$date[1])
      })

      watchlist_data2 <- watchlist_data %>%
        select(symbol, symbol_move, symbol_move_return, close)
      watchlist_dt <- datatable(
        watchlist_data2,
        options = list(
          rowCallback = JS('
            function(nRow, aData) {
              if (Number(aData[3]) < 0) {
                $(nRow).css("background-color", "#ff99bb")
              } else if (Number(aData[3]) > 1) {
                $(nRow).css("background-color", "#d9e8a7")
              }
          }')
        ),
        colnames = c("sym", "$", "%", "close")
      )
      output$watchlist <- DT::renderDataTable(
        watchlist_dt
      )
    }
  )
}

Another example: modules\vix_value_box_mod.R

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library(shiny)

vixValueBoxUI <- function(id) {
  ns <- NS(id)
  tagList(
    valueBoxOutput(ns("vix_score"))
  )
}

vixValueBoxServer <- function(id) {
  moduleServer(id, function(input, output, session) {
    vix <- reactive(
      tq_get(
        "^VIX",
        from = lubridate::today() - 7,
        to = lubridate::today() + lubridate::days(1)
      ) %>%
        slice_tail(n = 1) %>%
        mutate(
          symbol = "VIX",
          close = round(close, digits = 2)
        ) %>%
        select(close)
    )

    vix_subtitle <- "VIX"


    output$vix_score <- renderbs4ValueBox({
      # 0-15: This can indicate a certain amount of optimism in the market as well as very low volatility.
      if (vix() >= 0 & vix() <= 15) {
        vix_subtitle <-
          paste0("VIX: ", vix(), " certain amount of optimism and very low volatility 🐮")
        vix_subtitle2 <-
          paste0("Certain amount of optimism and very low volatility 🐮")
        color <- "success"
        icon <- "happy"
        # 15-25: This can indicate that there is a certain amount of volatility, but nothing extreme.
      } else if (vix() > 15 & vix() <= 25) {
        vix_subtitle <-
          paste0("VIX: ", vix(), " certain amount of volatility 🦬")
        vix_subtitle2 <-
          paste0("Certain amount of volatility 🦬")
        color <- "success"
        color <- "success"
        icon <- "happy"
        # 25-30: This can indicate that there is a certain amount of market turbulence and volatility is increasing.
      } else if (vix() > 25 & vix() <= 30) {
        vix_subtitle <-
          paste0("VIX: ", vix(), " certain amount of market turbulence and volatility is increasing volatility ✈️")
        vix_subtitle2 <-
          paste0("Certain amount of market turbulence and volatility is increasing volatility ✈️")
        color <- "warning"
        icon <- "sad"
        # 30 and over: This can indicate that the market is highly volatile and there may be some extreme swings soon.
      } else if (vix() > 30) {
        vix_subtitle <-
          paste0("VIX: ", vix(), " highly volatile and extreme swings 🐻")
        vix_subtitle2 <-
          paste0("Highly volatile and extreme swings 🐻")
        color <- "danger"
        icon <- "skull"
      }
      bs4ValueBox(
        value = tags$p(paste("VIX: ", vix()), style = "font-size: 150%;"),
        subtitle = vix_subtitle2,
        color = color,
        icon = ionicon(icon)
      )
    })
  })
}

Conclusion

This structure keeps my Shiny applications modular, maintainable, and scalable. By separating UI logic, server logic, global functions, utility functions, and modules, I ensure better readability and reusability across projects.

Credits

Pictures

  1. Glow by Jill Wellington
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© 2009 - 2025 Anthony Quoc Anh Doan - Ramblings of a Happy Scientist

Desiderata by Max Ehrmann

Go placidly amid the noise and the haste, and remember what peace there may be in silence. As far as possible without surrender be on good terms with all persons. Speak your truth quietly and clearly; and listen to others, even to the dull and the ignorant, they too have their story. Avoid loud and aggressive persons, they are vexations to the spirit.

If you compare yourself with others, you may become vain or bitter; for always there will be greater and lesser persons than yourself. Enjoy your achievements as well as your plans. Keep interested in your own career, however humble; it is a real possession in the changing fortunes of time.

Exercise caution in your business affairs, for the world is full of trickery. But let not this blind you to what virtue there is; many persons strive for high ideals, and everywhere life is full of heroism. Be yourself. Especially do not feign affection. Neither be cynical about love; for in the face of all aridity and disenchantment it is as perennial as the grass. Take kindly the counsel of the years, gracefully surrendering the things of youth.

Nurture strength of spirit to shield you in sudden misfortune. But do not distress yourself with dark imaginings. Many fears are born of fatigue and loneliness. Beyond a wholesome discipline, be gentle with yourself. You are a child of the universe, no less than the trees and the stars; you have a right to be here. And whether or not it is clear to you, no doubt the universe is unfolding as it should.

Therefore, be at peace with God, whatever you conceive Him to be. And whatever your labors and aspirations in the noisy confusion of life, keep peace in your soul. With all its sham, drudgery and broken dreams; it is still a beautiful world. Be cheerful.

Strive to be happy.

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