How to dynamically update a selectizeInput?

Question

I am attempting to dynamically update filters in my shiny app. For example, if one selects California as a state then the only cities that populate in the City filter should be cities from California.

However, if I select California, the code shows all the cities in the dataframe regardless if they are in California or not.

I have tried various attempts but am unsure of how to update the filtered data without creating a continuous loop or selecting a filter and it resetting itself. The original data has roughly twelve columns I am looking to filter.

library(shiny)
library(data.table)
library(DT)

ui <- 
  fluidPage(
    
    # Application title
    titlePanel("Display CSV Data"),
    
    # Sidebar layout with input and output definitions
    sidebarLayout(
      
      # Sidebar panel for inputs
      sidebarPanel(
        # No input needed if the CSV is static
        
        # Use selectizeInput for filtering
        uiOutput("filter_ui")
      ),
      
      # Main panel for displaying output
      mainPanel(
        # Output: DataTable
        dataTableOutput("table")
      )
    )
  )

server <- 
  function(input, output, session) {
    
    # Read the CSV file into a data table and display as a DataTable
    cols_to_filter <- c('state', 'city', 'county')
    
    data <- reactive({
      data.table(
        state = c("California", "California", "California", "New York", "New York", "Texas", "Texas", "Texas"),
        city = c("Los Angeles", "San Francisco", "Claremont", "New York", "Buffalo", "Houston", "Austin", "San Marcos"),
        county = c("Los Angeles", "San Francisco", "Los Angeles", "New York", "Erie", "Harris", "Travis", "Hays"),
        population = c(3979576, 883305, 36161, 8336817, 256902, 2325502, 964254, 65053)  # Fictional population figures
      )
    })
    
    observe({
      setkeyv(data(), cols_to_filter)
    })
    
    # Generate selectizeInput for filtering
    output$filter_ui <- renderUI({
      filter_inputs <- lapply(cols_to_filter, function(col) {
        selectizeInput(
          inputId = paste0("filter_", col),
          label = col,
          choices = c("", sort(unique(data()[[col]]))),
          multiple = TRUE,
          options = list(
            placeholder = 'Select values'
          )
        )
      })
      
      do.call(tagList, filter_inputs)
    })
    
    # Filter the data table based on user selections
    filtered_data <- reactive({
      filtered <- data()
      
      for (col in cols_to_filter) {
        filter_values <- input[[paste0("filter_", col)]]
        if (length(filter_values) > 0) {
          filtered <- filtered[get(col) %in% filter_values]
        }
      }
      
      filtered
    })
    
    # Display the filtered data table
    output$table <- renderDataTable({
      filtered_data()
    })
  }

shinyApp(ui = ui, server = server)

Answer 1

You need to run updateSelectizeInput if one of the SelectizeInput receives a selection. Therefore you could include the code below: The first lapply attaches an observeEvent to all SelectizeInput and the lapply inside contains the updates.

lapply(
  X = cols_to_filter,
  FUN = function(colChanged) {
    observeEvent(input[[paste0("filter_", colChanged)]], {
      lapply(
        X = cols_to_filter,
        FUN = function(colToChange) {
          updateSelectizeInput(
            inputId = paste0("filter_", colToChange),
            choices = filtered_data()[[colToChange]],
            selected = input[[paste0("filter_", colToChange)]]
          )
        }
      )
    }, ignoreNULL = FALSE)
  }
)