trouble with mutate and group by in reactive values in shiny

Question

My shiny app will be used in the following way:

1. upload csv (tab 1)
2. select variables of interest (tab 2)
3. press button for operation (tab 2)

The operation is to count the number of unique observations (factor A) by group (trial_id) to estimate the degree of freedom for a particular trial (those interested in stats will know what I mean). However, I have not been able to group by using reactive values (selected variables of a csv file). I've tried a lot of things. rlang, etc. Even when the output is printed, the group_by function is not able to properly get the correct grouping. Any help would be greatly appreciated.

# Packages library =================================================

# load or install packages
library(shiny)
library(shinydashboard)
library(tidyverse)
library(data.table)
library(rlang)


# Tab Content =========================================================================

# Upload file tab ----------------------------------------------

upload_tab <-     tabItem(tabName = "FileUpload",
                          titlePanel("Uploading Files"),
                          sidebarPanel(
                            fileInput('file1', 'Choose file to upload',
                                      accept = c('text/csv',
                                                 'text/comma-separated-values',
                                                 'text/tab-separated-values',
                                                 'text/plain','.csv','.tsv')),
                            checkboxInput("header", "Header", TRUE),
                            radioButtons("sep", "Separator",
                                         choices = c(Comma = ",",
                                                     Semicolon = ";",
                                                     Tab = "\t"),
                                         selected = ","),
                            radioButtons("quote", "Quote",
                                         choices = c(None = "",
                                                     "Double Quote" = '"',
                                                     "Single Quote" = "'"),
                                         selected = '"')),
                          mainPanel(
                            DT::dataTableOutput('contents')
                          )
)


# Estimator tab --------------------------------------------------------------------
estimator_tab <-  tabItem(tabName = "Estimator",
                          fluidPage(
                            fluidRow(
                              box(title = "Design", width = 6, solidHeader = T, status = "primary",
                                  fluidRow(
                                    column(8,
                                           sliderInput('alpha',"Significance level ?? ",0.05, min = 0.01, max = 0.10))),
                                  br(),
                                  br(),
                                  actionButton("go_button", "Estimate"),
                                  br(),
                                  br(),
                                  br(),
                                  uiOutput("downloadData")),
                              box(title = "Column ID", width = 6, solidHeader = T, status = "primary",
                                  column(8, selectInput("trial_id", "Trial ID", NULL),
                                         selectInput("factor_A", "Factor A", NULL),
                                         selectInput("replicates", "Replicates", NULL)))),
                            br(),
                            mainPanel(
                              DT::dataTableOutput('contents1')
                            )
                          )
)



# SideBar content =========================================================================

sideBar_content <- dashboardSidebar(
  sidebarMenu(
    menuItem("Upload File", tabName = "FileUpload"),
    menuItem("Estimator", tabName = "Estimator")
  )
)

# BODY content ------------------------------------------------------------------------------

body_content <- dashboardBody(
  tabItems(
    upload_tab,
    estimator_tab
  )
)

# UI =========================================================================

ui <-  dashboardPage(
  dashboardHeader(title = "Test"),
  ## Sidebar content
  sideBar_content,
  ## Body content
  body_content,
  ## Aesthetic
  skin = "blue"
)

# Server =========================================================================
server <- function(input, output,session) {
  
  
  data<-reactive({
    if(is.null(input$file1))
      return()
    inFile <- input$file1
    df <- read.csv(inFile$datapath,
                   header = input$header,
                   sep = input$sep,
                   quote = input$quote)
  }) 
  
  rv <- reactiveValues(data = data,
                       trial_id = NULL,
                       replicates = NULL)
  
  
  output$contents <- DT::renderDataTable({
    DT::datatable(data(),
                  options = list(
                    "pageLength" = 40))
  })
  
  # observe variable names from csv file
  observe({
    value <- names(data())
    updateSelectInput(session,"trial_id", choices = value)
    updateSelectInput(session,"replicates", choices =value)
    updateSelectInput(session,"factor_A", choices = value)
  })
  
  
  observeEvent(input$trial_id, {
    rv$trial_id <- data()[,input$trial_id]
  })
  observeEvent(input$replicates, {
    rv$replicates <- data()[,input$replicates]
  })
  observeEvent(input$factor_A, {
    rv$factor_A <- data()[,input$factor_A]
  })

  
  data_filtered<- reactive({
    dt<- data() %>% group_by(rv$trial_id) %>% dplyr::mutate(n_factor_A = length(unique(rv$factor_A)))
  })
  
  addData <- eventReactive(input$go_button, {
    return(data_filtered() %>% group_by(rv$trial_id) %>% dplyr::mutate(df_error = (n_factor_A-1)*(replicates-1)))}
  
  output$contents1 <- DT::renderDataTable({
      DT::datatable(addData(),
                    options = list("pageLength" = 40))
  })
 
  
}

# Run shiny app ---------------------------------------------------------------------------

shinyApp(ui, server)

Data

file<-c(structure(list(trial_id = c(2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 
2L, 2L, 2L, 2L, 2L, 1L, 1L, 1L, 1L, 1L, 4L, 4L, 4L, 4L, 4L, 4L
), factor_A = c(1L, 2L, 3L, 4L, 5L, 6L, 7L, 8L, 9L, 10L, 11L, 
12L, 13L, 14L, 1L, 2L, 3L, 4L, 5L, 1L, 2L, 3L, 4L, 5L, 6L), replicates = c(3L, 
3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 5L, 5L, 5L, 
5L, 5L, 4L, 4L, 4L, 4L, 4L, 4L), means = c(57.5, 22.5, 17.5, 
25, 5, 2, 3, 2, 12.5, 25, 3, 2.8, 1, 0.5, 64.1, 80.7, 83, 84.4, 
83.7, 25, 20, 25, 26, 27, 28), letters = c("a", "b", "bc", "b", 
"de", "e", "e", "e", "cd", "d", "e", "e", "e", "e", "a", "b", 
"b", "b", "b", "a", "b", "a", "a", "a", "a")), class = "data.frame", row.names = c(NA, 
-25L)))```