r - table command fails with shiny input variable -

i'm creating first shiny app, works fantastic when using ggplot2 using other base r or vcd plots has me stuck. i'd user able select tabling variable , view resulting mosaic or association plot. server code fails @ table command. things i've tried commented out below.

thanks help.

library(shiny) library(shinydashboard) library(vcd)  header = dashboardheader(title = 'min reproducible example') sidebar = dashboardsidebar() body = dashboardbody(   fluidrow(plotoutput('plot'), width=12),   fluidrow(box(selectinput('factor', 'select factor:', c('os', 'gender'))))     )   ui = dashboardpage(header, sidebar, body)  server = function(input, output){   set.seed(1)   df = data.frame(condition = rep(c('a','b','c','d'), each = 300),                    conversion = c(sample(c('convert','not-convert'), 300,      replace = true, prob = c(0.9, 0.1)),                               sample(c('convert','not-convert'), 300, replace = true, prob = c(0.7, 0.3)),                               sample(c('convert','not-convert'), 300, replace = true, prob = c(0.5, 0.5)),                              sample(c('convert','not-convert'), 300, replace = true, prob = c(0.2, 0.8))),                   gender = sample(c('m','f'), 1200, replace = true),                   os = rep(sample(c('web','ios','android'), 1200, replace = true), times = 2))        #tried       #table1 = reactive({       #  with(df, table(condition, conversion, input$factor))        #})    output$plot = renderplot({     #fails here:     table1 = with(df, table(condition, conversion, input$factor))      #also tried these     #table1 = with(df, table(condition, conversion,     as.character(isolate(reactivevaluestolist(input$factor)))))     #also tried table1 = with(df, table(condition, conversion, input$factor))     #also tried table1 = table(df$condition, df$conversion, paste0('df$', input$factor))        #then want categorical plots     assoc(table1, shade=true)     #or mosaicplot(table1, shade=true)   }) }   shinyapp(ui, server) 

an easy fix use 'starts_with' dplyr in select() statement on input variable

library('dplyr')  output$plot = renderplot({    df <- select(df, condition, conversion, tmp_var = starts_with(input$factor))    table1 = with(df, table(condition, conversion, tmp_var))    mosaicplot(table1, shade=true)    }) }