Hello shiny app gives me error in reactive expression

Question

Hello i am trying to reproduce an example of shiny apps of RStudio in this link: https://shiny.rstudio.com/articles/tabsets.html The shinyapp gives error with the d() reactive expression, and i try to change the expression but gives me error: The code is:

library(shiny)

Define UI for random distribution app ----

ui <- fluidPage(

# App title ----
titlePanel("Tabsets"),

# Sidebar layout with input and output definitions ----
sidebarLayout(
    
    # Sidebar panel for inputs ----
    sidebarPanel(
        
        # Input: Select the random distribution type ----
        radioButtons("dist", "Distribution type:",
                     c("Normal" = "norm",
                       "Uniform" = "unif",
                       "Log-normal" = "lnorm",
                       "Exponential" = "exp")),
        
        # br() element to introduce extra vertical spacing ----
        br(),
        
        # Input: Slider for the number of observations to generate ----
        sliderInput("n",
                    "Number of observations:",
                    value = 500,
                    min = 1,
                    max = 1000)
        
    ),
    
    # Main panel for displaying outputs ----
    mainPanel(
        
        # Output: Tabset w/ plot, summary, and table ----
        tabsetPanel(type = "tabs",
                    tabPanel("Plot", plotOutput("plot")),
                    tabPanel("Summary", verbatimTextOutput("summary")),
                    tabPanel("Table", tableOutput("table"))
        )
        
    )
)

)

Define server logic for random distribution app ----

server <- function(input, output) {

# Reactive expression to generate the requested distribution ----
# This is called whenever the inputs change. The output functions
# defined below then use the value computed from this expression
d <- reactive({
    dist <- switch(input$dist,
                   norm = rnorm,
                   unif = runif,
                   lnorm = rlnorm,
                   exp = rexp,
                   rnorm)
    
    dist(input$n)
})

# Generate a plot of the data ----
# Also uses the inputs to build the plot label. Note that the
# dependencies on the inputs and the data reactive expression are
# both tracked, and all expressions are called in the sequence
# implied by the dependency graph.
output$plot <- renderPlot({
    dist <- input$dist
    n <- input$n
    
    hist(d(),
         main = paste("r", dist, "(", n, ")", sep = ""),
         col = "#75AADB", border = "white")
})

# Generate a summary of the data ----
output$summary <- renderPrint({
    summary(d())
})

# Generate an HTML table view of the data ----
output$table <- renderTable({
    d()
})

}

Create Shiny app ----

shinyApp(ui, server)

The error when i run the app is: Warning: Error in dist: invalid arguments reactive:d [C:\Users\pruebas\Documents\Shiny_examples\tabs/app.R#63]

Can someone help i am trying to learn my first apps looking in articles at RStudio, but this one is wrong, and it is supposed to be done to teach people like me. I also dearch in github but i found the same code.Thank you.

Answer 1

Your app works fine.

Are you saving it as two separate files, i.e, ui.r and server.r, or a single file, i.e. app.r?

Your code is set up for it being saved as two separate files, but the error looks like you might have saved it as a single file.

Try saving it as two files:

ui.r

ui <- fluidPage(
    
    # App title ----
    titlePanel("Tabsets"),
    
    # Sidebar layout with input and output definitions ----
    sidebarLayout(
        
        # Sidebar panel for inputs ----
        sidebarPanel(
            
            # Input: Select the random distribution type ----
            radioButtons("dist", "Distribution type:",
                         c("Normal" = "norm",
                           "Uniform" = "unif",
                           "Log-normal" = "lnorm",
                           "Exponential" = "exp")),
            
            # br() element to introduce extra vertical spacing ----
            br(),
            
            # Input: Slider for the number of observations to generate ----
            sliderInput("n",
                        "Number of observations:",
                        value = 500,
                        min = 1,
                        max = 1000)
            
        ),
        
        # Main panel for displaying outputs ----
        mainPanel(
            
            # Output: Tabset w/ plot, summary, and table ----
            tabsetPanel(type = "tabs",
                        tabPanel("Plot", plotOutput("plot")),
                        tabPanel("Summary", verbatimTextOutput("summary")),
                        tabPanel("Table", tableOutput("table"))
            )
            
        )
    )
    
)

server.r

server <- function(input, output) {
    
    # Reactive expression to generate the requested distribution ----
    # This is called whenever the inputs change. The output functions
    # defined below then use the value computed from this expression
    d <- reactive({
        dist <- switch(input$dist,
                       norm = rnorm,
                       unif = runif,
                       lnorm = rlnorm,
                       exp = rexp,
                       rnorm)
        
        dist(input$n)
    })
    
    # Generate a plot of the data ----
    # Also uses the inputs to build the plot label. Note that the
    # dependencies on the inputs and the data reactive expression are
    # both tracked, and all expressions are called in the sequence
    # implied by the dependency graph.
    output$plot <- renderPlot({
        dist <- input$dist
        n <- input$n
        
        hist(d(),
             main = paste("r", dist, "(", n, ")", sep = ""),
             col = "#75AADB", border = "white")
    })
    
    # Generate a summary of the data ----
    output$summary <- renderPrint({
        summary(d())
    })
    
    # Generate an HTML table view of the data ----
    output$table <- renderTable({
        d()
    })
    
}