R shiny selectInput to update value of a variable in source script, the variable is used to compute the model output plotted by the app

Question

I am building a shiny application which visualises the output of a complex model. The model is in a script which is sourced by the shiny app. I want to change one input of the model calculation with selectInput and plot the output model accordingly.

Below is a simplied version of the model's source script and the app.

model.R

#data of the model 
yellow_data <- c (10,28,14,40)
green_data <- c(20,40,50,90)
red_data <- c(50,50,50,80)

third_data <- c(30,32,3100,500)

data_model <- data.frame(yellow_data, green_data, red_data)

#the variable that should be updated by selectInput in the app.R
selected_data <- "yellow_data"

#the model output which should change according to changes in selected_data
model_output <- union(data_model[[selected_data]] * 200, third_data)

I want to change the value of the variable selected_data from the app.

app.R

library(shiny)

source("model.R")


ui <- fluidPage(
  
selectInput(inputId = "select_data", label = "SELECT DATA", choices = c("Yellow" = "yellow_data",
                                                                          "Green" = "green_data",
                                                                          "Red" = "red_data")),  
  plotlyOutput(outputId = "plot_model_output")
)

server <- function(input, output, session) {
  
  output$plot_model_output <- renderPlotly({ 
    
    selected_data_Change <- reactive({
      switch(input$select_data,
             "Yellow" = "yellow_data",
             "Green" = "green_data",
             "Red" = "red_data") 
    })
    
    selected_data <<- selected_data_Change()
       
    fig <- plot_ly(x = ~c(1:8), y = ~model_output, name = 'model output', type = 'scatter', mode ='lines')
   fig
  
  })
}
shinyApp(ui, server)

As you can see in app.R, I tried to update with selectInput the global variable selected_data which is used to compute model_output in model.R, which is sourced in app.R.

I would like the model_output to update and reflect according to selectInput.

I really hope you can help. Thank you

Answer 1

Perhaps you are looking for this

ui <- fluidPage(
  
  selectInput(inputId = "select_data", label = "SELECT DATA", choices = c("Yellow" = "yellow_data",
                                                                          "Green" = "green_data",
                                                                          "Red" = "red_data")),  
  plotlyOutput(outputId = "plot_model_output")
)

server <- function(input, output, session) {
  
  output$plot_model_output <- renderPlotly({ 
    
    #the model output which should change according to changes in selected_data
    model_output <- c(data_model[,as.character(input$select_data)]*200, third_data)
    
    fig <- plot_ly(x = ~c(1:8), y = ~model_output, name = 'model output', type = 'scatter', mode ='lines')
    fig
    
  })
}
shinyApp(ui, server)