CODEWITHSUNDEEP
rshiny
LearneR
LearneR

Reputation: 2531

Unable to deduce how to connect ui.R and server.R with an R script to run in the background

I was trying to follow suggestions given by a commenter (named: warmoverflow) in a question I posted yesterday: How to pass values from input boxes of shiny UI back into the variables in an R script and run it?

I decided to try the approach he proposed firstly in a short example. So, I created an R script mathops.R containing a function with minor math operations. It is as follows:

mathops.R:

mathops <- function(a,b) {
  print(paste0("Addition of two number is: ", a+b))
  print(paste0("Multiplication of two number is: ", a*b))
}

I developed a UI with two text boxes from which input will taken for the above mentioned varaibles a and b and also an action button to display the output. It is as follows:

ui.R:

library(shiny)
shinyUI(fluidPage(
  headerPanel("Inputting from Interface to Script"),

  sidebarPanel( 
    #'a' input
    textInput(inputId = "a", 
              label = h4("Enter a:"), 
              value = ""),

    textInput(inputId = "b", 
              label = h4("Enter b:"), 
              value = ""),

    actionButton(inputId = "input_action", label = "Show Inputs")),



  mainPanel( 
    h2("Input Elements"))
    textOutput("td"))


))

and now as he suggested, I was trying to develop the code for server.R file:

server.R:

library(shiny)
source(mathops.R)

shinyServer(function(input, output) {

  a <- eventReactive( input$input_action, {
    input$a 
  })

  b <- eventReactive( input$input_action, {
    input$b
  })

  output$td <- renderDataTable({
    mathops()
  })

}

But here is where I'm facing an impasse. I just couldn't think of how to connect that mathops.R script into server.R file so that it will take the input coming from the input boxes on the UI and pass those values into the variables a and b of the mathops() function in the R script shown above.

I'm new to shiny. What am I missing or misunderstanding here? How to solve this situation?

Please help!

Thanks.

Upvotes: 0

Views: 1617

Answers (2)

Xiongbing Jin
Xiongbing Jin

Reputation: 12087

Here is a working version with some changes from your original code. As pointed out in the other answer, there are a few errors in your code. In addition, I changed textOutput to htmlOutput. In server.R, I put all code inside the observeEvent environment.

In general, your method in your R script needs to return something suitable for process in server.R. For example, in this case, it returns a string, which server.R renders as text, and ui.R in turn renders as HTML.

Any variable/data that is accessible in server.R (including any files that it source) can be displayed in the ui. What you need is (1) a suitable render method to render this data in server.R (2) a suitable output container to hold the output display in ui.R

ui.R

library(shiny)

shinyUI(fluidPage(
    headerPanel("Inputting from Interface to Script"),

    sidebarPanel( 
        #'a' input
        numericInput(inputId = "a", 
                  label = h4("Enter a:"), 
                  value = 3),

        numericInput(inputId = "b", 
                  label = h4("Enter b:"), 
                  value = 4),

        actionButton(inputId = "input_action", label = "Show Inputs")),

    mainPanel( 
        h2("Input Elements"),
        htmlOutput("td")),
        # use dataTableOuput to display the result of renderDataTable. Just like the render methods, there are many output methods available for different kind of outputs. See Shiny documentation.
        dataTableOutput("table")


))

server.R

library(shiny)
source("mathops.R")

shinyServer(function(input, output) {        

    observeEvent(input$input_action, {
        a = input$a
        b = input$b
        output$td <- renderText({
            mathops(a,b)
        })
    })
    # Use renderDataTable to convert mat2 to a displayable object. There are many other render methods for different kind of data and output, you can find them in Shiny documentation
    output$table <- renderDataTable(data.frame(mat2))

})

mathops.R

mathops <- function(a,b) {
    return(paste0("Addition of two number is: ", a+b, br(), "Multiplication of two number is: ", a*b))
}

mat1 <- matrix(sample(1:16), ncol=4)
mat2 <- matrix(sample(1:25), ncol=5)

Upvotes: 2

mlegge
mlegge

Reputation: 6913

You had to do a couple things:

  1. Switch from using textInput to numericInput in your ui.R
  2. Your mainPanel arguments were not being parsed correctly
  3. You needed to use renderPrint instead of renderDataTable if you are going to be using printed text
  4. You can call a and b as reactive objects, but mathops is just a regular function:

Note: I moved the mathops function definition into the server.R for simplicity

ui.R

library(shiny)
shinyUI(fluidPage(
  headerPanel("Inputting from Interface to Script"),

  sidebarPanel(

    numericInput(inputId = "a",
              label = h4("Enter a:"),
              value = ""),

    numericInput(inputId = "b",
              label = h4("Enter b:"),
              value = ""),

    actionButton(inputId = "input_action", label = "Show Inputs")),

  mainPanel(
    h2("Input Elements"),
    textOutput("td")
    )
))

server.R

library(shiny)

mathops <- function(a, b) {
  print(paste0("Addition of two number is: ", a + b))
  print(paste0("Multiplication of two number is: ", a * b))
}

shinyServer(function(input, output) {

  a <- eventReactive( input$input_action, {
    input$a
  })

  b <- eventReactive( input$input_action, {
    input$b
  })

  output$td <- renderPrint({
    mathops(a(), b())
  })

})

Upvotes: 1

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