How to use the result of using reactive function as input in ui? - r shiny

Question

I used a reactive function on the server to create a data frame.

And I want to express the unique vector of one column of this data frame as selectinput in the UI.

ex)

DATA<-data.frame(ID, NAME)

####server#####
DATAFRAME<-reactive({DATA[DATA$ID %in% input$ID,})

####UI######
selectizeInput("name",label="name:",choices=unique(DATAFRAME$NAME))

In other words, I want to show a list of Names for data that has been refined once by ID in advance.

Answer 1

In order to react to changes in the reactive expression DATAFRAME you can use an observer and update the list of names with updateSelectizeInput (as pointed out by @MrFlick).

library(shiny)

ui <- fluidPage(
    titlePanel("Widget Dependencies Sample App"),
    selectizeInput("IdSelect", "Choose ID", "N/A"), # IDs to select from
    selectizeInput("IdName", "Choose Name", "N/A"), # Names depend on selected ID
    tableOutput("IdDatatable") # show the whole data set to understand what happens
)

server <- function(input, output, session) {
  ID   <- paste("ID", 1:3, sep = "_")
  NAME <- LETTERS[1:(3*5)]
  DATA <- data.frame(ID, NAME)
  updateSelectizeInput(session, "IdSelect", choices = unique(ID))

  DATAFRAME <- reactive({DATA[DATA$ID %in% input$IdSelect, ]})

  observe({
   updateSelectizeInput(session, "IdName", choices = unique(DATAFRAME()$NAME))
  })

  output$IdDatatable <- renderTable(DATA)
}

shinyApp(ui = ui, server = server)

However, if you need the reactive expression DATAFRAME only once, you can make the code even simpler. In that case, you wouldn't observe a DATAFRAME that reacts to changes in a widget. You can omit the DATAFRAMEand observe the input widget directly. This observer generates a filtered vector of Names and changes the choices in the selectizeInput with only one observer.

observe({
    Names <- DATA$NAME[DATA$ID %in% input$IdSelect]
    updateSelectizeInput(session, "IdName", choices = unique(Names))
})