title: Shiny not detecting input in output
body: <p>If I run the following code, everything runs fine:</p>
  
  <pre><code>    library(dplyr)
      library(tidyr)
      library(shiny)
  
      id &lt;- 1:100
      gender &lt;- sample(c('M','F'), 100, replace=TRUE)
      age &lt;- sample(18:22, 100, replace=TRUE)
      ethnicity &lt;- sample(c('W','B','H','A','O'), 100, replace = TRUE)
      grade &lt;- sample(LETTERS[1:4], 100, replace=TRUE)
      df &lt;- cbind(id,gender,age,ethnicity,grade) %&gt;% as.data.frame()
  
      list1 &lt;- list("id"="id","gender"="gender","age"="age","ethnicity"="ethnicity","grade"="grade")
      list2 &lt;- list("id"="id","gender"="gender","age"="age","ethnicity"="ethnicity","grade"="grade")
  
      ui &lt;-fluidPage(
  
        selectInput("picker1", "PICKER 1", choices = list1, selected = "gender"),
        selectInput("picker2", "PICKER 2", choices = list2, selected = "grade"),
        tableOutput("crosstabs")
  
      )
  
      server &lt;- function(input,output,session){
  
        output$crosstabs &lt;- renderTable({
  
          t&lt;-df %&gt;% select_all() %&gt;% select(-id) %&gt;%
            pivot_longer(cols = input$picker1) %&gt;%
            count(name,value, grade) %&gt;% pivot_wider(names_from = grade, values_from = n)
          t
        })
  
      }
  
      shinyApp(ui,server)
  </code></pre>
  
  <p>But when I update <code>output$crosstabs</code> to include <code>input$picker2</code>, it returns an error. I'm rather confused, as I'm using the same structure, but simply with <code>grade</code> swapped out for <code>input$picker2</code>:</p>
  
  <pre><code>output$crosstabs &lt;- renderTable({
  
      t&lt;-df %&gt;% select_all() %&gt;% select(-id) %&gt;%
        pivot_longer(cols = input$picker1) %&gt;%
        count(name,value, input$picker2) %&gt;% pivot_wider(names_from = input$picker2, values_from = n)
      t
    })
  </code></pre>
  
  <p>What exactly is happening here?</p>