Demo updateselectInput() and also introducing observeEvent() function

DESCRIPTION

Title: Use case - Demo updateselectInput() and also introducing observeEvent() function
Description: Powered by R, Shiny, and RStudio.
License: GPL-3
Author: Abhinav Agrawal
DisplayMode: Showcase
Tags: R, R Shiny,updateselectInput(), observeEvent()
Type: Shiny

global.r

# global.r
# Defining a dummy dataframe for the sake of demo
# The dataset / objects/ variables from global.r is accessible to both the server.r and ui.r files
# placed in the working directory
# creating dataframe object with 3 variables namely, Year, Month & Person name
# this dataframe might not make sense but just for example
data = data.frame(Year=c("2002","2003","2004","2003","2001","2002", "2001"), 
                  Month = c("Jan", "Feb", "Mar", "Jan", "Dec", "Jan", "Nov"),
                  Name =c("Sam", "Paul", "James", "Ana","Rose", "Juan", "Tim"),
                  row.names=NULL, stringsAsFactors = FALSE)

server.r

library(shiny)

shinyServer(function(session, input, output){
  
#   observerEvent() function can be used in cases when an action needs to be performed based on event
#   In this case we want the second selectInput() choices to be updated based on the changes in 
#   the first select input()
  
  
  # Update based on the year change event
  # bascially populate the months corresponding to the year
  observeEvent(
    input$Year,
updateSelectInput(session, "Month", "Month", 
                  choices = data$Month[data$Year==input$Year]))
  
  # Update as soon as Month gets populated according to the year and month selected
  observeEvent(
    input$Month,
updateSelectInput(session, "Name", "Name", 
    choices = data$Name[data$Month==input$Month & data$Year==input$Year]))
  
  # just to display the dataset we created in global.r 
output$dataset <- renderTable({
  data
})
  
  })

ui.r

library(shiny)
shinyUI(fluidPage(
  titlePanel("Demo updateselectInput() and also introducing observeEvent() function"),
  # data is a dummy dataset which is coming from global.r
  # using the variables from data dataset we are populating the selectinput
  selectInput("Year", "Year", choices = unique(data$Year)),
  
  # Second select input for month - empty - no choice to display.
  # This is done intentionally as the idea is to populate this selectinput using 
  # updateselectinput on the loading of app or change in the year selectinput choice
  selectInput("Month", "Month", choices = "", selected = ""),
  
  # Third select input for Person - empty - no choice to display
  # This is done intentionally as the idea is to populate this selectinput using 
  # updateselectinput on the loading of app or change in the year and/or month selectinput choice
  selectInput("Name", "Name", choices = "", selected = ""),
  tableOutput("dataset")
  ))

Hi Nabeelah it is almost impossible to help you without providing a reproducible example and code you using