Update three different inputs based on sum of values R shiny - r

Question

I have four user inputs in my ShinyApp such that:
The first input (total_price) is always present
Optional input for rrsp which allows users to input a value (max 35,000)
Optional input for fthbi which allows users to select a value up to 10%
Other payment for cash which allows user to input a value
In my code, total_input and cash are numericInput, rrsp and fthbi are checkBoxInput + conditionalPanel
total_price is independent of the other three. However, the other other three summed up and can not exceed 20% of total_price i.e. rrsp + fthbi * total_price + cash <= total_price*0.2. How can I achieve this - basically as any of the inputs change, the limits of the remaining inputs (in the order mentioned above) should change as well.
CODE
ui <- fluidPage(
titlePanel(
'My App'
),
sidebarLayout(
sidebarPanel = sidebarPanel(
numericInput(
inputId = 'total_price',
label = 'Total Price',
value = 200000,
min = 200000
),
# Use RRSP for down-payment
checkboxInput(
inputId = 'use_rrsp',
label = 'Use RRSP?',
value = F
),
# If using RRSP, select amount to use
conditionalPanel(
condition = "input.use_rrsp == true",
numericInput(
inputId = 'rrsp', label = 'RRSP Amount?',value = 25000, min = 0, 35000
)
),
# Use first time home buyer incentive?
checkboxInput(
inputId = 'use_fthbi',
label = 'Use FTHBI?',
value = F
),
# If using FTHBI, select % to use
conditionalPanel(
condition = "input.use_fthbi == true",
sliderInput(
inputId = 'fthbi', label = 'FTHBI Percent',
step = 1, min = 0, max = 10, value = 0, post = '%'
)
),
# Cash Downpayment
numericInput(
inputId = 'cash', label = 'Cash Payment', value = 0, min = 0, max = 40000
)
),
mainPanel = mainPanel(
textOutput('main_text')
)
)
)
server <- function(input, output, session){
output$main_text <- renderText({
sprintf('Sample Text')
})
}
shinyApp(ui, server)
I've tried playing around with updateSliderInput and reactiveUI but haven't been successful..
Update
Here's the logic:
by default rrsp and ftbhi are not selected, so cash can be set to 20% of total_price
Once rrsp is selected, it should begin with a default value of 25000. The max. value for rrsp is 35000 which is less than 20% of the min. allowable total_value. If some value for cash is selected that would bring rrsp + cash > total_price, the cash value should be updated such taht the total is 20% max.
Once ftbhi is selected, the default value should be zero (updated code now). The max. value for this should be updated based on the rrsp value (if already selected) else it should be 10%.
cash should get updated as other values are selected, input.

Answer 1

Aou are on the right track in using the update* functions. I am not going to implement the complete logic yet the snippet below should point you in the right direction:
# Basic usage
library("shiny")
library(shinyWidgets)
ui <- fluidPage(
titlePanel(
'My App'
),
sidebarLayout(
sidebarPanel = sidebarPanel(
numericInput(
inputId = 'total_price',
label = 'Total Price',
value = 200000,
min = 200000
),
# Use RRSP for down-payment
checkboxInput(
inputId = 'use_rrsp',
label = 'Use RRSP?',
value = F
),
# If using RRSP, select amount to use
conditionalPanel(
condition = "input.use_rrsp == true",
numericInput(
inputId = 'rrsp', label = 'RRSP Amount?',value = 25000, min = 0, 35000
)
),
# Use first time home buyer incentive?
checkboxInput(
inputId = 'use_fthbi',
label = 'Use FTHBI?',
value = F
),
# If using FTHBI, select % to use
conditionalPanel(
condition = "input.use_fthbi == true",
sliderInput(
inputId = 'fthbi', label = 'FTHBI Percent',
step = 1, min = 0, max = 10, value = 0, post = '%'
)
),
# Cash Downpayment
numericInput(
inputId = 'cash', label = 'Cash Payment', value = 0, min = 0, max = 40000
)
),
mainPanel = mainPanel(
textOutput('main_text')
)
)
)
server <- function(input, output, session){
output$main_text <- renderText({
sprintf('Sample Text')
})
observe({
# check that the input exists, is not null etc. check ?req()
req(input$cash)
if(input$cash > 0)
updateSliderInput(session = session,
inputId = 'fthbi',
max = round(40000 / input$cash))
})
}
shinyApp(ui, server)
Just wrap your update function inside of observe. However, you should be carefull that you do not implement a infinite loop. In this case it is an option to determine each value, safe it in reactiveValues and use these to update your inputs.