Passing calculations run in renderPlotly to be shown in table below graph (without global variables)

What is the best way to take calculations generated in one output and print it as a datatable below the graph. Take the old faithful data where you've defined the "bins" value and you want the user to see what it equals without recalculating it, and without assigning a global variable?

library(shiny)
library(tidyverse)
library(plotly)
library(DT)

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


    # Sidebar with a slider input for number of bins 
    sidebarLayout(
        sidebarPanel(
            sliderInput("bins",
                        "Number of bins:",
                        min = 1,
                        max = 50,
                        value = 30)
        ),

        # Show a plot of the generated distribution
        mainPanel(
           plotOutput("distPlot"),
           DT::dataTableOutput("bin_val")
        )
    )
)

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

    output$distPlot <- renderPlot({
        # generate bins based on input$bins from ui.R
        x    <- faithful[, 2]
        bins <- seq(min(x), max(x), length.out = input$bins + 1)

        # draw the histogram with the specified number of bins
        hist(x, breaks = bins, col = 'darkgray', border = 'white',
             xlab = 'Waiting time to next eruption (in mins)',
             main = 'Histogram of waiting times')
    })
    output$bin_val <- DT::renderDT(datatable(bins))
}

# Run the application 
shinyApp(ui = ui, server = server)

Not sure if what you're asking for specifically can be done. You need to save bins somewhere since the output of distPlot is a plot and any variables inside of that function can not be accessed directly.

Below is an option to instantiate a reactiveValues object. Then inside your renderPlot function you can save bins to that object.

In this case since bins is a vector you need to convert it to a data.frame in order for DT::datatable to render the table properly.

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

  output$distPlot <- renderPlot({
    # generate bins based on input$bins from ui.R
    x    <- faithful[, 2]
    rv$bins <- seq(min(x), max(x), length.out = input$bins + 1) # set "bins" to rv

    # draw the histogram with the specified number of bins
    hist(x, breaks = rv$bins, col = 'darkgray', border = 'white',
         xlab = 'Waiting time to next eruption (in mins)',
         main = 'Histogram of waiting times')
  })
  
  output$bin_val <- DT::renderDT({
    validate(need(!is.null(rv$bins), "No data"))
    datatable(data.frame(bins = rv$bins))
  })
}

Another option would be to use a reactive to compute the number of bins outside of renderPlot. Additionally I moved the "creation" of x to a reactive too:

library(shiny)
library(DT)

# Define UI for application that draws a histogram
ui <- fluidPage(
  sidebarLayout(
    sidebarPanel(
      sliderInput("bins",
        "Number of bins:",
        min = 1,
        max = 50,
        value = 30
      )
    ),
    mainPanel(
      #plotOutput("distPlot"),
      DT::dataTableOutput("bin_val")
    )
  )
)

server <- function(input, output) {
  x <- reactive({
    faithful[, 2]
  })

  bins <- reactive({
    seq(min(x()), max(x()), length.out = input$bins + 1)
  })

  output$distPlot <- renderPlot({
    hist(x(),
      breaks = bins(), col = "darkgray", border = "white",
      xlab = "Waiting time to next eruption (in mins)",
      main = "Histogram of waiting times"
    )
  })
  output$bin_val <- DT::renderDT(
    datatable(data.frame(bins = bins()))
  )
}

shinyApp(ui = ui, server = server)