R Shiny app seems to hang when generating data - r

Question

Colleagues,
I'm creating a Shiny app that can generate a data set with user-defined properties. The intended data-generation function can take some time, so I've substituted a very simple one.
My problem is that the app seems to just hang, or nothing happens at all, when I hit the GO button.
DEBUG in Rstudio shows nothing, and reactlog also gives no information.
Similar questions on this stackoverflow forum are more than 8 years old, and suggestions don't seem to work either.
I'm sure the solution is head-slapping simple but, right now, I'm lost.
Any suggestions from those more knowledgeable than this Shiny newbie?
## generate data set with user-defined parameters
## load libraries
library(shiny)
library(ggplot2)
library(DT)
##
options(shiny.reactlog = TRUE)
# Define UI
ui <- fluidPage(
# Application title
titlePanel("Synthesise data"),
# Sidebar
sidebarLayout(
sidebarPanel(
## Sample size
numericInput("sample_n", "Sample size", 30,
min = 10, max = 300, step = 1
),
h4("Desired scale moments"),
numericInput("target_mean", "Target mean", 4),
numericInput("target_sd", "Target st dev", 1),
hr(style = "border-top: 1px solid #000000;"),
actionButton("goButton", "Go!"),
actionButton("goChart", "show chart"),
),
mainPanel(
h4("generated data"),
# table of generated data
DT::dataTableOutput("mytable"),
# Show a plot of the generated distribution
plotOutput("resultPlot")
)
)
)
# Define server logic
server <- function(input, output) {
mytable <- reactive(input$goButton, {
## substituting data-gen function that can take some time
mydata <- rnorm(sample_n, target_mean, target_sd) |>
data.frame()
colnames(mydata) <- "scale"
# saveRDS(mydata, file = "generatedData.RDS")
output$mytable <- DT::renderDataTable(DT::datatable({
mydata
}))
})
myplot <- eventReactive(input$goChart, {
output$resultPlot <- renderPlot({
ggplot(mydata, aes(x = scale)) +
geom_density()
})
})
}
# Run the application
shinyApp(ui = ui, server = server)

Answer 1

Few code errors here :
forgot input$ when using sample_n, target_mean and target_sd in server
put some output definition inside eventReactive or reactive is a terrible habit
reactive is not used like you did. EventReactive is what you needed here.
Here is a corrected version of you code
library(shiny)
library(ggplot2)
library(DT)
ui <- fluidPage(
titlePanel("Synthesise data"),
sidebarLayout(
sidebarPanel(
numericInput("sample_n", "Sample size", 30,
min = 10, max = 300, step = 1
),
h4("Desired scale moments"),
numericInput("target_mean", "Target mean", 4),
numericInput("target_sd", "Target st dev", 1),
hr(style = "border-top: 1px solid #000000;"),
actionButton("goButton", "Go!"),
actionButton("goChart", "show chart"),
),
mainPanel(
h4("generated data"),
DT::dataTableOutput("mytable"),
plotOutput("resultPlot")
)
)
)
server <- function(input, output) {
mydata <- eventReactive(input$goButton, {
mydata <- data.frame(scale = rnorm(input$sample_n, input$target_mean, input$target_sd))
return(mydata)
})
output$mytable <- DT::renderDataTable(DT::datatable(
mydata()
))
output$resultPlot <- renderPlot({
input$goChart
isolate(ggplot(mydata(), aes(x = scale)) +
geom_density())
})
}
shinyApp(ui = ui, server = server)