How to pass a data frame from UI to Server in an R Shiny Module?

Question

This is a follow up of this question: How to pass values from ui to server in a shiny module

In the minimum working example below of an R Shiny Module, I can use the function send_value_to_server() to send a value from UI to SERVER.

However, I cannot find a way to send more complex data structures like a dataframe, is there a way to do that?

library(shiny)

module_ui <- function(id, value_to_send) {
    
    ns <- shiny::NS(id)
        
    send_value_to_server <- function(id, value) {
    
        shiny::selectInput(
          inputId = id,
          label = "If you can see this, you forgot shinyjs::useShinyjs()", 
          choices = value, 
          selected = value, 
          multiple=TRUE
        ) |> shinyjs::hidden()
    
    }  
    
    shiny::tagList( 
    
        shinyjs::useShinyjs(),  # Set up shinyjs
        
        send_value_to_server(id = ns("value_to_send"), value = value_to_send),
    
        shiny::verbatimTextOutput(ns("text_out"))
        
    )    
}

module_server <- function(id) {
  moduleServer(id, function(input, output, session) {
  
    value_received <- reactive(input$value_to_send) 
    
    output$text_out <- renderPrint({
        paste("value passed from ui to server:", value_received())
    })  
    
  })
}

ui <- fluidPage(
    module_ui("test", value_to_send = 10)
)  

server <- function(input, output, server) {
    module_server("test")
}
  

shinyApp(ui, server)

Answer 1

In this example app, you can send a dataframe to the server module, mutate it and display as a table, all inside the module.

library(shiny)
library(tibble)
library(dplyr)

selectUI <- function(id, values) {
    tagList(
        tableOutput(NS(id, 'table'))
        )
    
}

selectServer <- function(id, my_df) {
    moduleServer(id, function(input, output, session) {
        # make some complex calculation with values from the input
        df <- reactive({mutate(my_df(), values_squared = x^2)})
        # now we can make the module return an object (like a regular function), in this case a df.
        output$table <- renderTable({
            df()
        })
    })
}





ui <- fluidPage(
    sidebarLayout(sidebarPanel(
    shiny::selectInput(
        inputId = "values",
        label = "Data for dataframe",
        choices = 1:10,
        selected = 1:5,
        multiple = TRUE
    )),mainPanel(
    selectUI("test", values = 1:10),
    verbatimTextOutput("print")
)))

server <- function(input, output, server) {
    df <- reactive({tibble(x = as.numeric(input$values))})
    selectServer("test", df)
    

}



shinyApp(ui, server)

Also, this way the module can react to changes in the reactive passed as as the argument, while the data passed to the ui will always be static.

Edit: If we really need to do it through the module UI, we can send the df as text and then parse it to construct a data frame. I do not recommend this method mainly for security reasons. (A malicious user can send arbitrary code to the server).

code:

library(shiny)

module_ui <- function(id, value_to_send) {
    
    ns <- shiny::NS(id)
    
    send_value_to_server <- function(id, value) {
        
        shiny::selectInput(
            inputId = id,
            label = "If you can see this, you forgot shinyjs::useShinyjs()", 
            choices = value, 
            selected = value, 
            multiple=TRUE
        ) |> shinyjs::hidden()
        
    }  
    
    shiny::tagList( 
        
        shinyjs::useShinyjs(),  # Set up shinyjs
        
        send_value_to_server(id = ns("value_to_send"), value = value_to_send),
        
        shiny::verbatimTextOutput(ns("text_out"))
        
    )    
}

module_server <- function(id) {
    moduleServer(id, function(input, output, session) {
        
        value_received <- reactive(eval(parse(text = input$value_to_send))) 
        
        output$text_out <- renderPrint({
            value_received()
        })  
        
    })
}

ui <- fluidPage(
    module_ui("test", value_to_send = 'structure(list(Sepal.Length = c(5.1, 4.9, 4.7, 4.6, 5), Sepal.Width = c(3.5, 
                                                                             3, 3.2, 3.1, 3.6), Petal.Length = c(1.4, 1.4, 1.3, 1.5, 1.4), 
                    Petal.Width = c(0.2, 0.2, 0.2, 0.2, 0.2), Species = structure(c(1L, 
                                                                                    1L, 1L, 1L, 1L), .Label = c("setosa", "versicolor", "virginica"
                                                                                    ), class = "factor")), row.names = c(NA, 5L), class = "data.frame")')
)  

server <- function(input, output, server) {
    module_server("test")
}


shinyApp(ui, server)