R Shiny - why are updates not immediate after changing sliders and inputs? - r

Question

I'm creating a version of a sample size and power calculator. After running the code, when selecting the option "Sample Size", any updates to the sample size are immediate after moving around sliders or other numeric Inputs. However for the option "Power" (both coming from the first "selectInput" option), updates are not immediate if at all occurring.
I'm not sure if the correct move forward is to use a reactive expression.
library(shiny)
library(pwr)
ui <- fluidPage(
titlePanel("Sample Size and Power Calculator"),
sidebarLayout(
sidebarPanel(
#What are we calculating?
selectInput(inputId = "type",
label = strong("Calculator Options"),
choices = c("Pick an Option",
"Power",
"Sample Size"),
selected = "Pick an Option"),
#Display only if Sample Size is selected, ask for necessary parameters
conditionalPanel(
condition = "input.type == 'Sample Size'",
#1. Standard Deviation
numericInput(inputId = "stddev",
label = "Standard Deviation",
value = 10,
min = 1,
max = 400,
step = 1),
#2. Power
sliderInput(inputId = "power",
label = "Power of Study",
min = 0.5,
max = 0.99,
value = 0.8,
step = 0.01),
h6("Power as a decimal not percentage."),
h6("(0.8 means 80% power)"),
#3. Alpha (Significance)
sliderInput(inputId = "alpha",
label = "Significance of Study",
min = 0.01,
max = 0.2,
value = 0.05,
step = 0.01),
h6("Significance of study is most traditionally 0.05 (5%)"),
#4. Meandiff (Difference Between Groups)
numericInput(inputId = "meandiff",
label = "Expected Difference Between Group Means",
value = 20),
#5. Alternative Test
selectInput(inputId = "alt",
label = strong("Alternative Test Options"),
choices = c("Two-Sided" = "two.sided",
"Upper" = "greater",
"Lower" = "less"),
selected = "Two-Sided"),
h6("If unsure, leave at 'Two-Sided'.")
),
#Display only if Power is selected, ask for necessary parameters
conditionalPanel(
condition = "input.type == 'Power'",
#1. Standard Deviation
numericInput(inputId = "stddev",
label = "Standard Deviation",
value = 10,
min = 1,
max = 400,
step = 1),
#2. Size Per Group
numericInput(inputId = "npergroup",
label = "Number per Group",
value = 120),
h6("Assuming equal number in each group, enter number for ONE group."),
#3. Alpha (Significance)
sliderInput(inputId = "alpha",
label = "Significance of Study",
min = 0.01,
max = 0.2,
value = 0.05,
step = 0.01),
h6("Significance of study is most traditionally 0.05 (5%)"),
#4. Meandiff (Difference Between Groups)
numericInput(inputId = "meandiff",
label = "Expected Difference Between Group Means",
value = 20),
#5. Alternative Test
selectInput(inputId = "alt",
label = strong("Alternative Test Options"),
choices = c("Two-Sided" = "two.sided",
"Upper" = "greater",
"Lower" = "less"),
selected = "Two-Sided"),
h6("If unsure, leave at 'Two-Sided'.")
)
),
#Output:
mainPanel(
textOutput(outputId = "intro"),
textOutput(outputId = "desc"),
conditionalPanel(
condition = "input.type == 'Sample Size'",
textOutput(outputId = "samplesize")
),
conditionalPanel(
condition = "input.type == 'Power'",
textOutput(outputId = "power")
)
)
)
)
server <- function(input, output) {
#Introductory Text
output$intro <- renderText({
"Select an option and adjust the sliders and parameters."
})
#Description of what has been chosen
output$desc <- renderText({
paste("You chose: ", input$type)
})
#If Sample Size is selected, what is the sample size
output$samplesize <- renderText({
paste("Sample Size Per Group for Two-Sample t-test for Mean Diff
Assuming Two Groups and Equal Variances: ",
as.character(ceiling(pwr.t.test(d = input$meandiff / input$stddev,
sig.level = input$alpha,
power = input$power,
type = "two.sample",
alternative = input$alt)$n)))
})
#If Power is selected, what is the power
output$power <- renderText({
paste("Power for Two-Sample t-test for Mean Diff Assuming Two Groups and
Equal Variances: ",
format(round(pwr.t.test(d = input$meandiff / input$stddev,
sig.level = input$alpha,
n = input$npergroup,
type = "two.sample",
alternative = input$alt)$power * 100, 2),
nsmall = 2))
})
}
shinyApp(ui = ui, server = server)

Answer 1

It would be ideal that all the input ids are unique. Below I added 2 for those duplicated input ids. All of them are in the power analysis. After this change, the code works.
library(shiny)
library(pwr)
ui <- fluidPage(
titlePanel("Sample Size and Power Calculator"),
sidebarLayout(
sidebarPanel(
#What are we calculating?
selectInput(inputId = "type",
label = strong("Calculator Options"),
choices = c("Pick an Option",
"Power",
"Sample Size"),
selected = "Pick an Option"),
#Display only if Sample Size is selected, ask for necessary parameters
conditionalPanel(
condition = "input.type == 'Sample Size'",
#1. Standard Deviation
numericInput(inputId = "stddev",
label = "Standard Deviation",
value = 10,
min = 1,
max = 400,
step = 1),
#2. Power
sliderInput(inputId = "power",
label = "Power of Study",
min = 0.5,
max = 0.99,
value = 0.8,
step = 0.01),
h6("Power as a decimal not percentage."),
h6("(0.8 means 80% power)"),
#3. Alpha (Significance)
sliderInput(inputId = "alpha",
label = "Significance of Study",
min = 0.01,
max = 0.2,
value = 0.05,
step = 0.01),
h6("Significance of study is most traditionally 0.05 (5%)"),
#4. Meandiff (Difference Between Groups)
numericInput(inputId = "meandiff",
label = "Expected Difference Between Group Means",
value = 20),
#5. Alternative Test
selectInput(inputId = "alt",
label = strong("Alternative Test Options"),
choices = c("Two-Sided" = "two.sided",
"Upper" = "greater",
"Lower" = "less"),
selected = "Two-Sided"),
h6("If unsure, leave at 'Two-Sided'.")
),
#Display only if Power is selected, ask for necessary parameters
conditionalPanel(
condition = "input.type == 'Power'",
#1. Standard Deviation
numericInput(inputId = "stddev2",
label = "Standard Deviation",
value = 10,
min = 1,
max = 400,
step = 1),
#2. Size Per Group
numericInput(inputId = "npergroup",
label = "Number per Group",
value = 120),
h6("Assuming equal number in each group, enter number for ONE group."),
#3. Alpha (Significance)
sliderInput(inputId = "alpha2",
label = "Significance of Study",
min = 0.01,
max = 0.2,
value = 0.05,
step = 0.01),
h6("Significance of study is most traditionally 0.05 (5%)"),
#4. Meandiff (Difference Between Groups)
numericInput(inputId = "meandiff2",
label = "Expected Difference Between Group Means",
value = 20),
#5. Alternative Test
selectInput(inputId = "alt2",
label = strong("Alternative Test Options"),
choices = c("Two-Sided" = "two.sided",
"Upper" = "greater",
"Lower" = "less"),
selected = "Two-Sided"),
h6("If unsure, leave at 'Two-Sided'.")
)
),
#Output:
mainPanel(
textOutput(outputId = "intro"),
textOutput(outputId = "desc"),
conditionalPanel(
condition = "input.type == 'Sample Size'",
textOutput(outputId = "samplesize")
),
conditionalPanel(
condition = "input.type == 'Power'",
textOutput(outputId = "power")
)
)
)
)
server <- function(input, output) {
#Introductory Text
output$intro <- renderText({
"Select an option and adjust the sliders and parameters."
})
#Description of what has been chosen
output$desc <- renderText({
paste("You chose: ", input$type)
})
#If Sample Size is selected, what is the sample size
output$samplesize <- renderText({
paste("Sample Size Per Group for Two-Sample t-test for Mean Diff
Assuming Two Groups and Equal Variances: ",
as.character(ceiling(pwr.t.test(d = input$meandiff / input$stddev,
sig.level = input$alpha,
power = input$power,
type = "two.sample",
alternative = input$alt)$n)))
})
#If Power is selected, what is the power
output$power <- renderText({
paste("Power for Two-Sample t-test for Mean Diff Assuming Two Groups and
Equal Variances: ",
format(round(pwr.t.test(d = input$meandiff2 / input$stddev2,
sig.level = input$alpha2,
n = input$npergroup,
type = "two.sample",
alternative = input$alt2)$power * 100, 2),
nsmall = 2))
})
}
shinyApp(ui = ui, server = server)