Shiny module for paging through a faceted ggplot2 plot

facet_page.r

# Create facet page slider module UI
facetPageUI <- function(id) {
  tagList(
    sliderInput(
      NS(id, "facet_page"),
      "Facet page:",
      value = 1,
      min = 1,
      max = 2,
      step = 1,
      pre = "Page ",
      ticks = FALSE
    )
  )
}

# Create module server for facet page slider
facetPageServer <- function(id, plot, facets, ncol = 4, nrow = 3) {
  moduleServer(id, function(input, output, session) {
    p_temp <- plot + facet_wrap_paginate(facets,
                                      ncol = ncol, nrow = nrow,
                                      page = input$facet_page)

    # Only use pagination when the number of facets exceeds 12; this keeps
    # the UI clean.
    if (n_pages(p_temp) > 1) {
      p <- p_temp
      updateSliderInput(inputId = "facet_page", max = n_pages(p_temp))
    } else {
      p <- plot + facet_wrap(facets, ncol = ncol, nrow = nrow)
    }

    list(
      plot = p,
      n_pages = n_pages(p_temp)
    )
  })
}

# Generate an app with facet page slider UI and server modules for testing and experimentation
facetPageApp <- function() {
  ui <- fluidPage(
    facetPageUI("facet_page"),
    plotOutput("plot")
  )
  server <- function(input, output, session) {
    output$plot <- renderPlot({
      p <- ggplot(iris, aes(Sepal.Width, Sepal.Length)) +
        geom_point()

      facet_page <- facetPageServer("facet_page", p, c("Species"), ncol = 1, nrow = 1)

      facet_page$plot
    })

  }
  shinyApp(ui, server)
}

facetPageApp()