10.3.2 Example and `isolate()`

[asadow]

The final example in section 10.3.2 behaves the same without isolate():

ui <- fluidPage(
  sidebarLayout(
    sidebarPanel(
      numericInput("n", "Number of colours", value = 5, min = 1),
      uiOutput("col"),
    ),
    mainPanel(
      plotOutput("plot")  
    )
  )
)

server <- function(input, output, session) {
  col_names <- reactive(paste0("col", seq_len(input$n)))

  output$col <- renderUI({
    map(col_names(), ~ textInput(.x, NULL, value = input[[.x]]))
  })

  output$plot <- renderPlot({
    cols <- map_chr(col_names(), ~ input[[.x]] %||% "")
    # convert empty inputs to transparent
    cols[cols == ""] <- NA

    barplot(
      rep(1, length(cols)), 
      col = cols,
      space = 0, 
      axes = FALSE
    )
  }, res = 96)
}

shinyApp(ui, server)

vs.

ui <- fluidPage(
  sidebarLayout(
    sidebarPanel(
      numericInput("n", "Number of colours", value = 5, min = 1),
      uiOutput("col"),
    ),
    mainPanel(
      plotOutput("plot")  
    )
  )
)

server <- function(input, output, session) {
  col_names <- reactive(paste0("col", seq_len(input$n)))

  output$col <- renderUI({
    map(col_names(), ~ textInput(.x, NULL, value = isolate(input[[.x]])))
  })

  output$plot <- renderPlot({
    cols <- map_chr(col_names(), ~ input[[.x]] %||% "")
    # convert empty inputs to transparent
    cols[cols == ""] <- NA

    barplot(
      rep(1, length(cols)), 
      col = cols,
      space = 0, 
      axes = FALSE
    )
  }, res = 96)
}

shinyApp(ui, server)