datatable filters update on the fly - shiny

Question

In the basic example below I would like to have all filters updated every time user add a filter.
ui :
library(shiny)
library(DT)
fluidPage(
fluidRow(
column(4,
DT::dataTableOutput("dt")
)
)
)
Server :
library(shiny)
shinyServer(function(input, output) {
df <- data.frame(var1 = c(rep("A",3),rep("B",3)), var2 = c("x","y","x","z","x","s"), var3 = c(1:6))
output$dt <- renderDataTable({
DT::datatable(df, filter = 'top')
})
})
When no filter applied :
When I apply filter on var1 to "A", s and z still remain in the suggested label in var2 filter even if there are no value to s or z

Answer 1

This is how I would do if I use selectInput for the filters. May not be the best solution, but it has always worked for me.
Code for ui.r
library(shiny)
library(DT)
fluidPage(
fluidRow(
column(4,selectizeInput("var1", label = "Var 1", choices = NULL, multiple = TRUE)),
column(4,selectizeInput("var2", label = "Var 2", choices = NULL, multiple = TRUE)),
column(4,selectizeInput("var3", label = "Var 3", choices = NULL, multiple = TRUE)),
column(4,DT::dataTableOutput("dt")
)
)
)
Code for server.R
library(shiny)
shinyServer(function(input, output, session) {
df <- data.frame(var1 = c(rep("A",3),rep("B",3)), var2 = c("x","y","x","z","x","s"), var3 = c(1:6))
updateSelectizeInput(session, 'var1', choices = sort(unique(df$var1)), server = TRUE)
updateSelectizeInput(session, 'var2', choices = sort(unique(df$var2)), server = TRUE)
updateSelectizeInput(session, 'var3', choices = sort(unique(df$var3)), server = TRUE)
filterData <- function(dataset){
df <- dataset
if (!is.null(input$var1)){
df <- df[which(df$var1 == input$var1),]
}
if (!is.null(input$var2)){
df <- df[which(df$var2 == input$var2),]
}
if (!is.null(input$var3)){
df <- df[which(df$var3 == input$var3),]
}
df
}
output$dt <- renderDataTable({
DT::datatable(filterData(df))
})
getwhich<-function(){
whichs<-which(df$var3 == df$var3)
if(!is.null(input$var1)){
whichs<-intersect(whichs,which(df$var1 %in% input$var1))
}
if(!is.null(input$var2)){
whichs<-intersect(whichs,which(df$var2 %in% input$var2))
}
if(!is.null(input$var3)){
whichs<-intersect(whichs,which(df$var3 %in% input$var3))
}
return(whichs)
}
observe({
w<-getwhich()
if(is.null(input$var1)){
updateSelectizeInput(session,"var1",choices=sort(unique(df$var1[w])))
}
})
observe({
w<-getwhich()
if(is.null(input$var2)){
updateSelectizeInput(session,"var2",choices=sort(unique(df$var2[w])))
}
})
observe({
w<-getwhich()
if(is.null(input$var3)){
updateSelectizeInput(session,"var3",choices=sort(unique(df$var3[w])))
}
})
})
Hope this helps.