【R-shiny基础-1】Welcome to Shiny

Shiny是一个能方便构建交互式网页应用的R包，出自Rsutio，在官网中有非常多的学习资料。有视频和文字教程，也有基础和进阶，更难得的是有其他开发者发布的产品，值得学习。

这里是shiny基础系列，旨在对shiny基本用法有所了解。当然重复语法不过多解释，更多记录下注意事项。

Lesson 1 - Welcome to Shiny
Lesson 2 - Layout the user interface
Lesson 3 - Add control widgets
Lesson 4 - Display reactive output
Lesson 5 - Use R scripts and data
Lesson 6 - Use reactive expressions
Lesson 7 - Share your apps

内置示例

shiny包有11个内置示例，基本覆盖了Shiny的工作方式，可以在Rstudio中一一运行，结合代码学习：

library(shiny)
runExample("01_hello")      # a histogram
runExample("02_text")       # tables and data frames
runExample("03_reactivity") # a reactive expression
runExample("04_mpg")        # global variables
runExample("05_sliders")    # slider bars
runExample("06_tabsets")    # tabbed panels
runExample("07_widgets")    # help text and submit buttons
runExample("08_html")       # Shiny app built from HTML
runExample("09_upload")     # file upload wizard
runExample("10_download")   # file download wizard
runExample("11_timer")      # an automated timer

shiny结构与运行

三部分结构：

ui：定义用户界面
server：构建应用程序
shinyApp函数：调用应用程序

运行方式：

三部分结构可放在一个脚本中（如app.R），直接运行脚本即可，方便共享代码；
创建app的目录（如my_app），ui.R和server.R分别放在其中，在外部运行shiny::runAPP("my_app")。

示例如下：

library(shiny)

# Define UI for app that draws a histogram ----
ui <- fluidPage(

  # App title ----
  titlePanel("Hello Shiny!"),

  # Sidebar layout with input and output definitions ----
  sidebarLayout(

    # Sidebar panel for inputs ----
    sidebarPanel(

      # Input: Slider for the number of bins ----
      sliderInput(inputId = "bins",
                  label = "Number of bins:",
                  min = 1,
                  max = 50,
                  value = 30)

    ),

    # Main panel for displaying outputs ----
    mainPanel(

      # Output: Histogram ----
      plotOutput(outputId = "distPlot")

    )
  )
)

# Define server logic required to draw a histogram ----
server <- function(input, output) {

  # Histogram of the Old Faithful Geyser Data ----
  # with requested number of bins
  # This expression that generates a histogram is wrapped in a call
  # to renderPlot to indicate that:
  #
  # 1. It is "reactive" and therefore should be automatically
  #    re-executed when inputs (input$bins) change
  # 2. Its output type is a plot
  output$distPlot <- renderPlot({

    x    <- faithful$waiting
    bins <- seq(min(x), max(x), length.out = input$bins + 1)

    hist(x, breaks = bins, col = "#75AADB", border = "white",
         xlab = "Waiting time to next eruption (in mins)",
         main = "Histogram of waiting times")

    })

}

shinyApp(ui = ui, server = server)

runAPP("my_app")默认正常模式展示，即没有脚本：

image.png

若想要学习代码，可用展示模式，runApp("my_app", display.mode = "showcase")：

image.png

Ref:
https://shiny.rstudio.com/tutorial/written-tutorial/lesson1/