You posted a comment on my post saying that you were having the same problem as me. It looks a little bit different, but I found a solution to my problem so I've posted the code below in case it helps you at all.
l <- NULL
l$name <- c('b','e','d','b','b','d','e','e','b','b')
l$age <- c(20,20,21,21,20,22,22,30,21,32)
l$gender <- c('Female', 'Female', 'Male', 'Female', 'Male','Male',
'Female','Male',"Female","Male")
l <- as.data.frame(l)
l$name <- as.character(l$name)
l$age <- as.numeric(l$age)
l$gender <- as.character(l$gender)
library(shiny)
server <- shinyServer(function(input,output){
assign('All Names',unique(sort(l$name)))
assign("All Ages", unique(sort(l$age)))
assign('All Genders', unique(sort(l$gender)))
data1 <- reactive(l[which(l$name %in% if(exists(input$name))
{get(input$name)}else{input$name}),])
output$table1 <- renderTable(data1())
output$text1 <- renderPrint(input$name)
data2 <- reactive(data1()[which(data1()$age %in% if(exists(input$age))
{get(input$age)}else{input$age}),])
output$table2 <- renderTable(data2())
data3 <- reactive(data2()[which(data2()$gender %in% if(exists(input$gender))
{get(input$gender)}else{input$gender}),])
output$table3 <- renderTable(data3())
output$Box1 = renderUI(
if((is.null(input$age)) & (is.null(input$gender))){
selectInput("name", "Choose Name", choices=c("All Names",unique(sort(l$name))), selected = input$name)
} else{selectInput("name", "Choose Name", choices=c("All Names",unique(l[l$gender %in% (if(exists(input$gender)){get(input$gender)}else{input$gender}) & l$age %in% (if(exists(input$age)){get(input$age)}else{input$age}) , "name"])), selected = input$name)
}
)
output$Box2 = renderUI(
if((is.null(input$name)) & (is.null(input$gender))){
selectInput("age", "Choose Age", choices=c("All Ages", unique(sort(l$age))), selected = input$age)
}else{selectInput("age", "Choose Age", choices=c("All Ages",unique(l[l$gender %in% (if(exists(input$gender)){get(input$gender)}else{input$gender}) & l$name %in% (if(exists(input$name)){get(input$name)}else{input$name}) , "age"])), selected = input$age)}
)
output$Box3 = renderUI(
if((is.null(input$name)) & (is.null(input$age))){
selectInput("gender", "Choose Gender", choices=c("All Genders", unique(sort(l$gender))), selected = input$gender)
}else{
selectInput("gender", "Choose Gender", choices=c("All Genders", unique(l[l$name %in% (if(exists(input$name)){get(input$name)}else{input$name}) & l$age %in% (if(exists(input$age)){get(input$age)}else{input$age}), "gender"])), selected = input$gender, multiple = TRUE)
}
)
})
ui <-shinyUI(fluidPage(
uiOutput("Box1"),
uiOutput("Box2"),
uiOutput("Box3"),
tableOutput("table3")
))
shinyApp(ui,server)