RShiny reactive error - r

Question

I am building a simple RShiny App that calculates sample size and power, but I keep getting this error message---
Warning: Error in .getReactiveEnvironment()$currentContext: Operation not allowed without an active reactive context. (You tried to do something that can only be done from inside a reactive expression or observer.)
I couldn't figure out how to fix it. This is my first time using RShiny. If anyone can help, I really appreciate that! Thanks a lot!
library(shiny)
ui <- fluidPage(
headerPanel("Power and Sample Size Calculator"),
fluidRow(column(12,
wellPanel(
helpText("Two proportions (equal sample size in each group) power/sample size analysis"),
selectInput (inputId = "choice",
label = " Please Choose What You Want To Calculate",
c("Power","Sample Size"),selected = NULL,
multiple = FALSE,
selectize = TRUE, width = NULL, size = NULL)
)),
column(4,
wellPanel(
conditionalPanel(
condition = "input$choice = Power",
numericInput (inputId = "tau",
label = "Effect Size",
value = "0.2",
min = 0, max =1),
numericInput (inputId = "n",
label = "Sample Size in Each Group",
value = "200",
min = 0,
max = 100000000),
sliderInput (inputId = "alpha",
label = "Significance Level ⍺= ",
value = "0.05",
min = 0.001, max = 0.10)),
conditionalPanel(
condition = "input$choice=Sample Size",
numericInput (inputId = "tau",
label = "Effect Size",
value = "0.2",
min = 0, max =1),
sliderInput (inputId = "alpha",
label = "Significance Level ⍺= ",
value = "0.05",
min = 0.001, max = 0.10),
numericInput (inputId = "beta",
label = "Power",
value = "0.8",
min = 0,
max = 1))
)
),
column(8,
wellPanel(
htmlOutput("Result")
))
))
server <- function(input, output) {
choice <- switch (input$choice,
"Power" = 1, "Sample Size" = 2)
output$Result <- renderUI({
if(choice==1){
final=reactive({pwr.2p.test(h = input$tau, n = input$n, sig.level = input$alpha, power = )
})
}
if(choice==2){
final=reactive({pwr.2p.test(h = input$tau, n = , sig.level = input$alpha, power = input$beta)
})}
HTML(final)
}
)
}
shinyApp(ui=ui, server=server)

Answer 1

I don't think it is required to have reactive for final. try this below.
it works for me, except for pwr.2p.test, looks like that is some function you are trying to use. Also, I did not understand why you had HTML(final), use of renderUishould generate html by default. Let me know how did it go. Good luck
server <- function(input, output) {
choice <- reactive({
switch(input$choice,"Power" = 1,"Sample Size" = 2)})
output$Result <- renderUI({
if (input$choice == 'Power') {
pwr.2p.test( h = input$tau,
n = input$n,
sig.level = input$alpha,
power = input$beta
)}
if (input$choice == 'Sample Size') {
pwr.2p.test( h = input$tau,
n = ,
sig.level = input$alpha,
power = input$beta
)}
})
}