Select and scale variables in shiny app dynamically - r

Question

I have a shiny app where I want the user to be able to select which variables to keep in the final data frame and then also select which variables to scale into a percent. I have this working, but I am running into a little puzzle. The problem is if the user decides they want to add an additional variable (or remove one), they have to redo the scaling. This could be a problem if my users have many columns they are working on. How can I keep the scaling work the user has already done, while allowing for the addition or removal of variables from the final data frame?
library(shiny)
library(tidyverse)
library(DT)
# Define UI
ui <- fluidPage(
checkboxGroupInput("select_var", label = "Select Variables"),
selectInput("scalescore", label = NULL, choices = c("")),
actionButton("scale", "Scale Scores"),
DT::dataTableOutput("table")
)
# Define server
server <- function(session, input, output) {
# define the reactive values
values <- reactiveValues(df_final = NULL)
# dynamically generate the variable names
observe({
vchoices <- names(mtcars)
updateCheckboxGroupInput(session, "select_var", choices = vchoices)
})
# dynamically generate the variables to scale
observe({
vchoices <- names(values$df_final)
updateSelectInput(session, "scalescore", choices = vchoices)
})
# select the variables based on checkbox
observe({
req(input$select_var)
df_sel <- mtcars %>% select(input$select_var)
values$df_final <- df_sel
})
observeEvent(input$scale, {
name <- rlang::sym(paste0(input$scalescore, "_scaled"))
values$df_final <- values$df_final %>% mutate(!!name := round(!!rlang::sym(input$scalescore)/max(!!rlang::sym(input$scalescore), na.rm = TRUE)*100, 1))})
output$table <- DT::renderDataTable(values$df_final)
}
# Run the application
shinyApp(ui = ui, server = server)

Answer 1

We will need to maintain a vector which tracks whether a variable was scaled or not. Here is how it's done,
library(shiny)
library(tidyverse)
library(DT)
# Define UI
ui <- fluidPage(
checkboxGroupInput("select_var", label = "Select Variables"),
selectInput("scalescore", label = NULL, choices = c("")),
actionButton("scale", "Scale Scores"),
DT::dataTableOutput("table")
)
server = function(input,output,session){
#Column names are static
names = colnames(mtcars)
# data scructure to store if the variable is scaled
is_scaled = logical(length(names))
names(is_scaled) = names #Set the names of the logical vector to the column names
#Update the checkbox with the column names of the dataframe
observe({
updateCheckboxGroupInput(session, "select_var", choices = names)
})
# Update the list of choices but dont include the scaled vaiables
observe({
vchoices <- names(data())
vchoices = vchoices[vchoices %in% names]
updateSelectInput(session, "scalescore", choices = vchoices)
})
#When the scle button is pressed, the vector which contains the list of scaled variables is updated
observeEvent(input$scale,{
if(is_scaled[[input$scalescore]]){
is_scaled[[input$scalescore]] <<- FALSE
}else{
is_scaled[[input$scalescore]] <<- TRUE
}
})
#Function to scale the variables
scale = function(x){
return(round(x/max(x,na.rm = T)*100,1))
}
data = reactive({
req(input$select_var)
input$scale #simply to induce reactivity
#Select the respective columns
df = mtcars%>%
select(input$select_var)
if(any(is_scaled[input$select_var])){
temp_vec = is_scaled[input$select_var] #Get a list of variables selected
true_vec = temp_vec[which(temp_vec)] #Check which ones are scaled
true_vec_names = names(true_vec) #Get the names of the variables scales
#Scale the variables respectively
df = df%>%
mutate_at(.vars = true_vec_names,.funs = funs(scaled = scale(.)))
}
return(df)
})
output$table = DT::renderDataTable(data())
}
# Run the application
shinyApp(ui = ui, server = server)
is_scaled tracks whether a particular column is scaled or not. When it is later selected, it is scaled if the value is TRUE in this vector.
Additional functionality is also added where if the scale button is pressed twice the scale column is removed.