How to display a simple dataframe with input in R Shiny

Question

I'm having trouble displaying a dataframe that depends on user input. I need to have users pick a number, do some very simple calculations based on those numbers, and display the resulting dataframe. Does this require reactive() or observe()? Or is my formatting just off?

Simple example that works if you remove the attempt to work with 'input$exp':

library(shiny)
shinyApp(
 ui = fluidPage(

   
   fluidRow(
     column(6, sliderInput("exp", label = h5("Change this"), min=2, max=5, value = 2)),
     
     column(12,
            tableOutput('table')
     )
   )
 ),
 server = function(input, output) {
   foo<-data.frame(matrix(ncol=8, nrow=1))
   colnames(foo)<-c('a', 'b', 'c', 'd', 'e', 'f', 'g', 'h')
   foo$a<-input$exp+2
   foo$b<-2
   foo$c<-3
   output$table <- renderTable(foo)
 }
)

TichPi · Accepted Answer · 2022-02-04 16:29:31Z

2

Method 1:

library(shiny)
shinyApp(
  ui = fluidPage(        
    fluidRow(
      column(6, sliderInput("exp", label = h5("Change this"), min=2, max=5, value = 2)),       
      column(12,
             tableOutput('table')
      )
    )
  ),
  server = function(input, output) {
    output$table <- renderTable({
      foo<-data.frame(matrix(ncol=8, nrow=1))
      colnames(foo)<-c('a', 'b', 'c', 'd', 'e', 'f', 'g', 'h')
      foo$a<-input$exp+2
      foo$b<-2
      foo$c<-3
      return(foo)
    })
  }
)

Method 2:

library(shiny)
shinyApp(
  ui = fluidPage(        
    fluidRow(
      column(6, sliderInput("exp", label = h5("Change this"), min=2, max=5, value = 2)),       
      column(12,
             tableOutput('table')
      )
    )
  ),
  server = function(input, output) {
    result <- eventReactive(input$exp, {
      foo<-data.frame(matrix(ncol=8, nrow=1))
      colnames(foo)<-c('a', 'b', 'c', 'd', 'e', 'f', 'g', 'h')
      foo$a<-input$exp+2
      foo$b<-2
      foo$c<-3
      return(foo)
    })  
    output$table <- renderTable({
      result()
    })
  }
)

edited Feb 4, 2022 at 16:29

answered Feb 4, 2022 at 5:50

TichPi

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2 Comments

Garret C Over a year ago

Thanks, that works. Any explanation why? If I just wanted to display 'input$exp+2' I can get that to work with renderText just fine without doing anything reactive. Why does that not require reactive but the dataframe does?

TichPi Over a year ago

@GarretC I just updated the code. Maybe Method 1 is what you want which do not need reactive things.

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