r - Warning messages when subsetting on integer variables -

i have small shiny application in i'm displaying variable names checkboxgroupinput , based on selection i'm subsetting data table variables , displaying it.

what observed when variable of integer type label selected, there warning message on rstudio console :

warning in formatc(x = c(36l, 29l, 20l, 25l, 48l, 42l, 19l, 26l, 36l, 39l,  :   class of 'x' discarded 

if change variable type character(in case label gone) in data.table warning goes away - these warning messages mean , how rid of them without change type of columns? here code :

 server.r   library(shiny)   dft<-data.table(name=c("a","b","c"),age=c(10l,12l,13l))   label(dft$name)<-"full name"   label(dft$age)<-"age of patient"   shinyserver(function(input, output) {      output$x<- renderui({      checkboxgroupinput("g1","g1label",names(dft))    })   output$y<- rendertable({     if (length(input$g1 > 0))      {subset(dft,select=c(as.vector(input$g1)))}   })  })   ui.r   library(shiny)   shinyui(fluidpage(      uioutput("x")  ,      tableoutput("y")   ))