Changing Numeric Inputs to 0 if Check Box is Unchecked - r

Question

I was wondering if it was possible to set the value of a numeric input via updateNumericInput to be equal to 0 if a checkbox is not clicked. Below is how my code is set up at the moment to generate the check boxes and numeric inputs. I had to use loops to create a dynamic number of check boxes and inputs due to the nature of the app so I would really appreciate any help linking the two while keeping the functionality.
Server file:
shinyServer(function(input, output, session) {
output$inputs1 <- renderUI({
numSliders <- input$sources
lapply(1:numSliders, function(i) {
numericInput(
inputId = paste0('slider1', i),
label = df[i,2],
value = df[i,3]*(input$budget)/100)
})
})
output$checks1 <- renderUI({
numSliders <- input$sources
lapply(1:numSliders, function(i) {
checkboxInput(
inputId = paste0('check1', i),
label = df[i,2],
value = TRUE
)
})
})
}
UI:
shinyUI(fluidPage(fluidRow(
sidebarLayout(
sidebarPanel(
column(5,numericInput("budget", "Budget", value = 0),
uiOutput("checks1")),
column(5,uiOutput("inputs1"))),
mainPanel()
)
)
)
)
Please let me know if there is any sort of workaround for this.
Thanks in advance!

Answer 1

Since you can only generate a finite number of widgets the easiest way of creating an observer for each checkboxInput is to create a global variable, say, max_widgets which gives an upper bound on widgets. You then restrict the maximal value of numericInput which controls a number of widgets to max_widgets (so input$sources) and require within renderUIs that
req(numSliders > 0 & numSliders <= max_widgets)
(I would use validate and need to inform the user that the number of widgets has to be non negative and is bound to max_widgets but in my shiny version there is a bug and validate doesn't work as supposed.)
You then create observers for each checkboxInput on the server side:
lapply(1:max_widgets, function(i) {
observeEvent(input[[paste0('check', i)]], {
print(paste0("update of numeric", i))
updateNumericInput(session, inputId = paste0('numeric', i),
value = 0)
})
})
Note that this will create observers for all possible checkboxes (checkboxes may not even exist - shiny won't complain :) )
This may not be perfect but, as said, you will have only one observer for each checkbox.
If you dynamically generate observers in a following way (without a global variable max_widgets)
observe({
lapply(1:input$sources, function(i) {
observeEvent(input[[paste0('check', i)]], {
print(paste0("numeric", i, " = ", input[[paste0('numeric', i)]]))
updateNumericInput(session, inputId = paste0('numeric', i),
value = 0)
})
})
it will work too but each time you will generate new widgets you will also create an observer for it. So you may get multiple observers for each checkboxInput!
If your app is small then it won't matter much but in general it may lead to bugs. You can easy deal with it but it makes the code slightly more complicated - there was a question that touched on this problem.
Full example:
library(shiny)
rm(list = ls())
max_widgets <- 15
server <- shinyServer(function(input, output, session) {
output$inputs1 <- renderUI({
numSliders <- input$sources
# My shiny version has a bug and can't use validate(need(...)) because
# it doesn't work as suppossed
req(numSliders > 0 & numSliders <= max_widgets)
lapply(1:numSliders, function(i) {
numericInput(
inputId = paste0('numeric', i),
# label = df[i,2],
paste0("Input ", i),
# value = df[i,3] * (input$budget) / 100)
value = i * (input$budget) / 100)
})
})
output$checks1 <- renderUI({
numSliders <- input$sources
req(numSliders > 0 & numSliders <= max_widgets)
lapply(1:numSliders, function(i) {
list(
checkboxInput(
inputId = paste0('check', i),
# label = df[i,2],
label = paste0("Checkbox ", i),
value = TRUE
),
br()
)
})
})
lapply(1:max_widgets, function(i) {
observeEvent(input[[paste0('check', i)]], {
print(paste0("update of numeric", i))
updateNumericInput(session, inputId = paste0('numeric', i),
value = 0)
})
})
})
ui <- shinyUI(fluidPage(fluidRow(
sidebarLayout(
sidebarPanel(
column(5,
numericInput("budget", "Budget", value = 0),
hr(),
br(),
uiOutput("checks1")
),
column(5,
numericInput("sources", "Sources", value = 0, min = 0, max = max_widgets),
hr(),
uiOutput("inputs1")
)
),
mainPanel()
)
)))
shinyApp(ui, server)