R shiny: Get table to only display the top x rows

Context: I'm trying to make a R shiny server which takes file uploads and displays it in a table in the UI. The file can either be in csv, txt or tsv, meaning read.csv() is not appropriate. Also the table output can change at anytime depending on the user's input of the radiobuttons to determine the delimiter.

Problem: I can't seem to make the table only display the top x number of rows from the file. Does anyone know any possible solutions?

Attempted solutions:

• I've tried using renderDataTable function, however it had an error saying that data() is needs to be a matrix or dataFrame. It doesn't make sense since read.table() function would return a dataframe(https://www.rdocumentation.org/packages/utils/versions/3.6.2/topics/read.table). And data <-reactive would mean data is a dataFrame.

Server

server <- function(input, output, session) {
  output$distPlot <- renderPlot({
    hist(rnorm(input$obs), col = 'darkgray', border = 'white')
  })
  
  observe({
    # DEFile from fileInput() function
    ServerDEFile <- req(input$DEFile)
    
    # extensions tool for format validation
    extDEFile <- tools::file_ext(ServerDEFile$datapath)
    if(is.null(input$DEFile)){return()
    }else{
      if (extDEFile == "txt") {
        label = paste("Delimiters for", extDEFile, "file")
        choice <-c(Comma=",", Semicolon=";", Tab="\t", Space=" ")
      }else if (extDEFile == "tsv") {
        label = paste("Delimiter: Tab")
        choice <- (Tab="\t")
      }else {
        label = paste("Delimiter: Comma")
        choice <- (Comma=",")
      }
      updateRadioButtons(session, "sepButton", label = label, choices = choice)
    }
  })
  
  # reactive converts the upload file into a reactive expression known as data
  data <- reactive({

    # DEFile from fileInput() function
    ServerDEFile <- input$DEFile

    # extensions tool for format validation
    extDEFile <- tools::file_ext(ServerDEFile$datapath)

    # file format checking
    req(ServerDEFile)
    # validate(need(extDEFile == c("csv", "tsv", "txt"), "Please upload a csv, tsv or txt file."))

    # convert data into file format
    if(is.null(extDEFile)){return()}

    read.table(file=ServerDEFile$datapath, sep=input$sepButton)
  })

  # creates reactive table called DEFileContent
  output$DEFileContent <- renderTable({
    if(is.null(data())){return ()}
    data()
  })

  # handles rendering of reactive object on tb on ui
  output$UIDEContent <- renderUI({
    tableOutput("DEFileContent")
  })
}

UI

library(shinyWidgets)
library(DT)
library(shiny)
ui <- fluidPage(
  titlePanel(title=div(img(src="ODClogo.png", height = 50), "OutDeCo")),

  #navbarPage is top menu bar
  navbarPage("",

             #tabPanel is each tab in the navbarPage
             # Assess DE tab
             tabPanel(
               title="Assess DE",
               dropdown(

                 # title of sidepanel
                 tags$h3("Options"),

                 # inputs in the sidepanel
                 fileInput("DEFile", "Choose DE File",
                           accept = c(
                             ".csv",
                             ".tsv",
                             ".txt"
                           )
                 ),

                 # button for selecting delimiter, default is nothing until file is selected and handled in server side
                 radioButtons(inputId = 'sepButton', label = 'Delimiter Selector', choices = c(Default=''), selected = ''),

                 # side panel characteristics
                 style = "gradient", icon = icon("cog"),
                 status = "primary", width = "300px",
                 animate = animateOptions(
                   enter = animations$fading_entrances$fadeInLeftBig,
                   exit = animations$fading_exits$fadeOutLeftBig
                 )
               ),

               navlistPanel(
                 tabPanel(
                   title="Cluster Genes",
                   "Cluster genes Page",

                   # Navigation Bar for types of plots inside cluster
                   tabsetPanel(
                     tabPanel(
                       title="View file",
                       mainPanel(
                         uiOutput("UIDEContent")
                       )

                     ),
                     tabPanel(
                       title="Plot 2"
                     ),
                     tabPanel(
                       title="Plot 3"
                     )
                   ),
                 ),
               ),
             )
  ),
)