Next reactive button for selectInput in shiny

Question

My code so far:

library(shiny)

plot_choices_temp <- c(
  "1. Overview" = "1. Overview",
  "2. Overview (2)" = "2. Overview (2)",
  "3. Daily cumulative mean temp." = "3. Daily cumulative mean temp."
)

plot_choices_pcp <- c(
  "1. Daily cumulative precip. (vs. percentiles)" = "1. Daily cumulative precip. (vs. percentiles)",
  "2. Daily cumulative precip. (vs. mean)" = "2. Daily cumulative precip. (vs. mean)",
  "3. Number of days with more than 25mm of precip." = "3. Number of days with more than 25mm of precip."
)

ui <- shiny::fluidPage(
  theme = shinythemes::shinytheme("spacelab"),
  
  # Application title
  shiny::titlePanel("AEMET OpenData"),
  
  # Sidebar panel
  shiny::sidebarLayout(
    shiny::sidebarPanel(
      width = 3,
      shiny::selectInput(
        inputId = "variable",
        label = "Variable",
        choices = c("Mean temperature (00h-24h)", 
                    paste0("Precipitation (07h-07h", "\u207A", "\u00B9", ")"))
      ),
      shiny::selectInput(
        inputId = "plot",
        label = "Metric",
        choices = NULL
      ),
      shiny::fluidRow(
        column(
          6,
          shiny::actionButton(
            inputId = "updatePlot",
            label = "Paint!"
          )
        ),
        column(
          6,
          shiny::actionButton(
            inputId = "nextPlot",
            label = "Next"
          )
        )
      )
    ),
    shiny::mainPanel(
      width = 9,
      shiny::textOutput("plot")
    )
  )
)

server <- function(input, output, session) {
  
  # Configure "Next" button
  observeEvent(input$nextPlot, {
    if (input$variable == "Mean temperature (00h-24h)") {
      plot_choices <- plot_choices_temp
    } else if (input$variable == paste0("Precipitation (07h-07h", "\u207A", "\u00B9", ")")) {
      plot_choices <- plot_choices_pcp
    }
    current_index <- match(input$plot, plot_choices)
    
    # Find next index within choices
    next_index <- current_index %% length(plot_choices) + 1
    
    # Establish next plot in the list
    updateSelectInput(session, "plot", selected = plot_choices[next_index][[1]])
  })
  
  # Update plot selection choices depending on variable (tmean, pcp...) selection
  observe({
    if (input$variable == "Mean temperature (00h-24h)") {
      plot_choices <- plot_choices_temp
    } else if (input$variable == paste0("Precipitation (07h-07h", "\u207A", "\u00B9", ")")) {
      plot_choices <- plot_choices_pcp
    }
    
    updateSelectInput(session, "plot", choices = plot_choices)
  })
  
  # Do not change plot until button is pressed
  text <- eventReactive(list(input$updatePlot, input$nextPlot), ignoreInit = TRUE, { 
    # Draw plot
    return(input$plot)
  })
  
  # Display plot
  output$plot <- shiny::renderPrint({
    print(text())
  })
  
}

shiny::shinyApp(ui = ui, server = server)

I want a "Next" button so that when it is pressed, the value of input$plot changes so that the next plot is painted. With my code only the selected option is changed in the UI but not internally.

For example, when having "Mean temperature (00h-24h)" as Variable, and "1. Overview" as Metric, if you press the Next button Metric changes to "2. Overview (2)" but internally input$plot = "1. Overview" (should also change to "2. Overview (2)")

Answer 1

Your eventReactive object is not changing after the update of input$plot. So, try this

 text <- eventReactive({input$updatePlot 
                         input$nextPlot
                         input$plot}, ignoreInit = TRUE, { 
    # Draw plot
    return(input$plot)
  })