Shiny: calculating standard deviation from an uploaded excel file - r

Question

I am trying to calculate the standard deviation of an Excel file loaded onto my Shiny App. I don't appear to be able to do so. When I put sd(output$contents) or sd(file1) it tends to crash the application. Here is what I have so far
For reference, the data I am uploading is univariate time series
I would be very grateful if someone would be able to help me out- I think it is a beginner problem! perhaps I am just viewing the file and not using it?
EDIT: the excel file always contains a single column of numbers, but the title and header may change. Therefore I would like to reference column A in the changing excel files.
ui <- fluidPage(
setBackgroundColor("ghostwhite"),
titlePanel(h1("title", style = "color:navy")),
p("subtitle"),
headerPanel(h3("Input data here", style = "color:navy")),
# Sidebar panel
sidebarLayout(
sidebarPanel( position =c("left"),
sliderInput("SL",
"ServiceScore",
min = 1.28, max = 3.09, value = 2.28),
numericInput("LT", "LT: weeks",0, min=0, max = 30),
fileInput('file1', 'MS, choose xlsx file',
accept = c(".xlsx")
),
br(),
actionButton("action_Calc", label = "Refresh & Calculate"), ),
# Main panel
mainPanel(h3( textOutput("SL"),
textOutput("LT"),
textOutput("SS"),
tableOutput('contents')
))))
server <- function(input, output) {
output$SL <- renderText({
paste("Your score", input$SL)})
output$LT <- renderText ({
paste( "Your LT is", input$LT)})
output$contents <- renderTable({
req(input$file1)
inFile <- input$file1
read_excel(inFile$datapath, 1)
})
values<- reactiveValues()
observe({
input$action_Calc
values$int<- isolate({
input$SL*sqrt(input$LT/4)*sd(**HERE IS WHERE I NEED THE SD of the EXCEL FILE**)
})})
output$SS <- renderText({paste("calculation is", values$int)})
}
shinyApp(ui, server)

Answer 1

Read the Excel file in a reactive conductor:
Data <- reactive({
req(input$file1)
inFile <- input$file1
read_excel(inFile$datapath, 1)
})
output$contents <- renderTable({
Data()
})
Now if you want the standard deviation of the first column:
values<- reactiveValues()
observe({
input$action_Calc
values$int <- isolate({
input$SL*sqrt(input$LT/4)*sd(Data()[[1]])
})
})
output$SS <- renderText({paste("calculation is", values$int)})