Shiny if else statement

Question

I am having problems using conditional statements in Shiny. I want the user select number of variable. If choose 1 variable then plot chart of 1 variable (ex density plot), if choose 2 variable then plot chart of 2 variables (ex scatter plot). I have tried a few ways, but the output is not as my expected. How can i use if else statement in Shiny server? Tks

UI

   df <- mtcars
    ui <- fluidPage(
        h1("My first app",
           style = 'color: green;
           font-style: italic'),
        hr(),
        fluidRow(
            sidebarPanel(
                radioButtons(inputId = "number",
                             label = "Select number of variable",
                             choices = c("1 variable" = 1,
                                         "2 variable" = 2)),
                selectInput(inputId = "x",
                            label = "Variable 1",
                            choices = names(df)),
                conditionalPanel(
                    condition = "input.number == 2",
                    selectInput(inputId = "y",
                                label = "Variable 2",
                                choices = names(df))
                    ) 
                ),
            column(8, plotOutput("plot"))
        ),
        hr(),
        plotOutput("plot") )

Server

server <- function(input, output, session){
    observeEvent(input$x, 
                 {updateSelectInput(session,
                                    inputId = "y",
                                    label = "Variable 2",
                                    choices = names(df)[names(df) != input$x])
                 })
    
    data <- reactive({
        if(input$number == 1){
            data <- df %>% 
                select(input$x)
        } else {
            data <- df %>% 
                select(input$x, input$y)
        }
    })
    
    output$plot <- renderPlot({
        if(input$number == 1){
            ggplot(data = data(),
                   x = get(input$x))+
                geom_density()
        } else {
            ggplot(data = data,
                   x = get(input$x),
                   y = get(input$y)) +
                geom_point()
        }
    })
}

shinyApp(ui = ui, server = server)

Ronak Shah · Accepted Answer · 2021-07-12T06:56:48.713

You can try the following code -

plotOutput("plot") was mentioned twice, removed it to include it only once.
We don't need to check for conditions while creating the dataset in reactive, handle it in the plot code itself.
Use .data to refer column names in ggplot code.

library(shiny)
library(ggplot2)

df <- mtcars
ui <- fluidPage(
  h1("My first app",
     style = 'color: green;
           font-style: italic'),
  hr(),
  fluidRow(
    sidebarPanel(
      radioButtons(inputId = "number",
                   label = "Select number of variable",
                   choices = c("1 variable" = 1,
                               "2 variable" = 2)),
      selectInput(inputId = "x",
                  label = "Variable 1",
                  choices = names(df)),
      conditionalPanel(
        condition = "input.number == 2",
        selectInput(inputId = "y",
                    label = "Variable 2",
                    choices = names(df))
      ) 
    ),
    column(8, plotOutput("plot"))
  )
)


server <- function(input, output, session){
  
  data <- reactive({
    df
  })

 observeEvent(input$x, 
               {updateSelectInput(session,
                                  inputId = "y",
                                  label = "Variable 2",
                                  choices = names(df)[names(df) != input$x])
               })
  
  output$plot <- renderPlot({
    
    if(input$number == 1){
      plot <- ggplot(data = data(), aes(x = .data[[input$x]])) + geom_density()
    } else {
      plot <- ggplot(data = data(),
             aes(x = .data[[input$x]], y = .data[[input$y]])) +
        geom_point()
    }
    plot
  })
}

shinyApp(ui = ui, server = server)

Tks @Ronak Shah . It's helpful to me – Kevin_Nguyen Jul 12 '21 at 07:08 — Kevin_Nguyen, Jul 12 '21 at 07:08

score 3 · Answer 2 · answered Jul 12 '21 at 06:53

You could use aes_string.
Another very important point is never to use the same output twice in UI:

df <- mtcars
library(ggplot2)
library(dplyr)

ui <- fluidPage(
  h1("My first app",
     style = 'color: green;
           font-style: italic'),
  hr(),
  fluidRow(
    sidebarPanel(
      radioButtons(inputId = "number",
                   label = "Select number of variable",
                   choices = c("1 variable" = 1,
                               "2 variable" = 2)),
      selectInput(inputId = "x",
                  label = "Variable 1",
                  choices = names(df)),
      conditionalPanel(
        condition = "input.number == 2",
        selectInput(inputId = "y",
                    label = "Variable 2",
                    choices = names(df))
      ) 
    ),
    column(8, plotOutput("plot"))
  ),
  hr() 
  # Never use output twice : the UI won't work!
  #plotOutput("plot") 
  )

server <- function(input, output, session){
  observeEvent(input$x, 
               {updateSelectInput(session,
                                  inputId = "y",
                                  label = "Variable 2",
                                  choices = names(df)[names(df) != input$x])
               })
  
  data <- reactive({
    if(input$number == 1){
      data <- df %>% 
        select(input$x)
    } else {
      data <- df %>% 
        select(input$x, input$y)
    }
  })
  
  output$plot <- renderPlot({
    cat(input$x)
    if(input$number == 1){
      ggplot(data = data())+
        geom_density(aes_string(x=input$x))
    } else {
      ggplot(data = data()) +
        geom_point(aes_string(x=input$x,y=input$y))
    }
  })
}

shinyApp(ui = ui, server = server)

`aes_string` allows to use directly the string returned by `input$x` or `input$y`, which isn't the case of `aes` — Waldi, Jul 12 '21 at 07:18

Shiny if else statement

2 Answers2