## Create a data frame of which information is used in creating (dynamical) control widgets
varnames <- names(iris[,1:4]) # names
varinit <- apply(iris[,1:4],2,median) # initival value used in slider
varmin <- apply(iris[,1:4],2,min) # min.
varmax <- apply(iris[,1:4],2,max) # max.

## dataframe
vardf <- data.frame(varnames,varmin,varmax,varinit)

ui <- fluidPage(
   checkboxGroupInput("ConditioningVariables", "Conditioning variables (choose one or more):",
                      varnames,inline = TRUE),
uiOutput("ControlWidgetsofConditioningVariables"),
   tableOutput("data")
)

server <- function(input, output, session) {

   output$ControlWidgetsofConditioningVariables <- renderUI({
      if (is.null(input$ConditioningVariables)){
         return()
      } else {
         selvarnames = sort(input$ConditioningVariables)
         selpos = sapply(selvarnames,function(x) which(varnames==x))
         # create a taglist of dynamic widgets
         ListofDynamicWidgets <- lapply(selpos, function(x){sliderInput(as.character(vardf[x,1]),
                                                          as.character(vardf[x,1]),
                                                          vardf[x,2],vardf[x,3],
                                                          vardf[x,4],.1)})
         do.call(tagList, ListofDynamicWidgets)
      }
   })
   ## filter data as per selected variables and their range
   ## this is where I'm kind of struck, I think I need to track number of variables (is list good idea?)
   ## and filter as per selected range of a specific variable
   newdata <- reactive({
      subset(iris)
   })
   output$data <- renderTable({ newdata() })
   }
shinyApp(ui, server)