Shiny example app with dynamic number of plots

app.r

max_plots <- 5

ui <- fluidPage(

  headerPanel("Dynamic number of plots"),

  sidebarPanel(
    sliderInput("n", "Number of plots", value=1, min=1, max=5)
  ),

  mainPanel(
    # This is the dynamic UI for the plots
    uiOutput("plots")
  )
)

server <- function(input, output) {

  # Insert the right number of plot output objects into the web page
  output$plots <- renderUI({
    plot_output_list <- lapply(1:input$n, function(i) {
      plotname <- paste("plot", i, sep="")
      plotOutput(plotname, height = 280, width = 250)
    })

    # Convert the list to a tagList - this is necessary for the list of items
    # to display properly.
    do.call(tagList, plot_output_list)
  })

  # Call renderPlot for each one. Plots are only actually generated when they
  # are visible on the web page.
  for (i in 1:max_plots) {
    # Need local so that each item gets its own number. Without it, the value
    # of i in the renderPlot() will be the same across all instances, because
    # of when the expression is evaluated.
    local({
      my_i <- i
      plotname <- paste("plot", my_i, sep="")

      output[[plotname]] <- renderPlot({
        plot(1:my_i, 1:my_i,
             xlim = c(1, max_plots),
             ylim = c(1, max_plots),
             main = paste("1:", my_i, ".  n is ", input$n, sep = "")
        )
      })
    })
  }
}

shinyApp(ui, server)

I wanted to add another use case to this excellent gist. In my case I wanted to generate a dynamic number of graphs based on the factor levels of a column from a user input file. See also https://stackoverflow.com/questions/75250661/generate-dynamic-number-of-plots-based-on-factor-levels-of-user-input-file/75251212#75251212

library(shiny)
library(data.table)
library(ggplot2)
library(dplyr)

ui <- fluidPage(
  
  headerPanel("Dynamic number of plots"),
  
  sidebarPanel(
    fileInput("fileIn", 
              "Load input file",
              multiple = F)
  ),
  
  mainPanel(
    uiOutput("plot1")
  )
)

server <- function(input, output) {
  
  getData <- reactive({
    req(input$fileIn)
    dataIn <- as.data.frame(fread(input$fileIn$datapath))
    dataIn$plotGroup <- make.names(dataIn$plotGroup)
    return(dataIn)
  })
  
  output$plot1 <- renderUI({
    plotOutputList <- lapply(unique(getData()$plotGroup),
                             function(i){
                               plotname <- paste("plot", i, sep = "_")
                               plotOutput(plotname)
                             })
    do.call(tagList, plotOutputList)
  })
  
  observe({
  for(i in unique(getData()$plotGroup)){
    local({
      iCurrent <- i
      plotname <- paste("plot", iCurrent, sep = "_")
      
      output[[plotname]] <- renderPlot({
        getData() %>%
          filter(plotGroup == iCurrent) %>%
        ggplot(aes(x = xGroup, y = yVar)) +
          geom_point()
      })
    })
  }})
}

shinyApp(ui, server)