Updating pickerInput based on radiobutton - r

Question

I want to be able to update the selection available in the pickerInput based upon the selection made in the radio button input. In the example below, I want the radio button "A", to give a pickerInput list of mtcars$cyl, whilst a picker input of "B" to give a picker input of mtcars$mpg
I have tried doing this using if statements, but I haven't got anywhere so far. Reproducible example below:
library(shiny)
library(leaflet)
library(shinyjs)
library(rgeos)
library(tidyverse)
library(openxlsx)
library(plotly)
library(shinyWidgets)
library(rgdal)
ui <- fluidPage(shinyjs::useShinyjs(),
fluidRow(column(
6,radioButtons("type", "Type:",
c("A" = "norm",
"B" = "unif")))),
fluidRow(column(
3,
pickerInput("regInput","Region",choices=unique(mtcars$cyl),
options = list(`actions-box` = TRUE),multiple = T,
selected = unique(mtcars$cyl)))))
server <- function (input, output, session) {
observeEvent(input$type,{
a_option <- input$regInput
if (a_option == "B") {
updatePickerInput(session = session,inputId = "regInput",
choices =unique(mtcars$mpg))}})
}
shinyApp(ui = ui, server = server)

Answer 1

As said in the other answer you need to observe input$type and update the picker input according to the values in it. Also, it's important to include an else statement, to be able to update the picker input when the user picks between the radio button choices multiple times. Finally, on the updatePickerInput you need to include the selected argument to maintain the behaviour as it is on the ui.
Here's the code doing what I've described above:
library(shiny)
library(shinyjs)
library(tidyverse)
library(shinyWidgets)
ui <- fluidPage(shinyjs::useShinyjs(),
fluidRow(
column(
6,
radioButtons("type",
"Type:",
c("A" = "norm",
"B" = "unif"))
)),
fluidRow(
column(
3,
pickerInput("regInput","Region",
choices=unique(mtcars$cyl),
options = list(`actions-box` = TRUE),
multiple = T,
selected = unique(mtcars$cyl))
))
)
server <- function (input, output, session) {
observeEvent(input$type,{
if (input$type == "unif") {
updatePickerInput(session = session,inputId = "regInput",
choices = unique(mtcars$mpg),
selected = unique(mtcars$mpg))
} else {
updatePickerInput(session = session,inputId = "regInput",
choices = unique(mtcars$cyl),
selected = unique(mtcars$cyl))
}
})
}
shinyApp(ui = ui, server = server)

Answer 2

The server has to listen to the right UI Element (ID = "type" for the radio buttons in question). Currently it observes an undefined element "dist".
Try changing
observeEvent(input$dist, { code })
to
observeEvent(input$type, { code })