r shinyapp: Change dataframe using numericInput - r

Question

I have the following shiny app, which consists of a numeric input and as outputs two ggplot-graphics.
library(shiny)
n <- 100
dat <- data.frame(var1 = round(rnorm(n, 50, 10),0),
var2 = sample(c("A", "B"), n, replace = TRUE))
# USER INTERFACE
ui <- fluidPage(
titlePanel("My Sample App"),
sidebarLayout(
sidebarPanel(
numericInput("n", "Number of cases", value=100)
),
mainPanel(
plotOutput("boxplot"),
plotOutput("distribution")
)
)
)
# SERVER
server <- function(input, output) {
output$boxplot <- renderPlot({
ggplot(data = dat, aes(x = var2, y = var1)) + geom_boxplot() + ggtitle("Boxplot")
})
output$distribution <- renderPlot({
ggplot(data = dat, aes(var1)) + geom_histogram() + ggtitle("Histogram")
})
}
# Run the application
shinyApp(ui = ui, server = server)
I've been trying to replace n = 10 with n = input$n. However it didn't work and I am unsure, where exactly I have to define the data.frame (inside the server function?). Can someone help please?

Answer 1

input$n is a reactive variable that can only be used in a reactive context. You can only define a reactive context in the server function, e.g. using reactive. Have a look here for an explanation.
library(shiny)
library(ggplot2)
# USER INTERFACE
ui <- fluidPage(
titlePanel("My Sample App"),
sidebarLayout(
sidebarPanel(
numericInput("n", "Number of cases", value=100)
),
mainPanel(
plotOutput("boxplot"),
plotOutput("distribution")
)
)
)
# SERVER
server <- function(input, output) {
dat <- reactive({
data.frame(var1 = round(rnorm(input$n, 50, 10),0),
var2 = sample(c("A", "B"), input$n, replace = TRUE))
})
output$boxplot <- renderPlot({
ggplot(data = dat(), aes(x = var2, y = var1)) + geom_boxplot() + ggtitle("Boxplot")
})
output$distribution <- renderPlot({
ggplot(data = dat(), aes(var1)) + geom_histogram() + ggtitle("Histogram")
})
}
# Run the application
shinyApp(ui = ui, server = server)