R Shiny: Using numeric output variable as the initial value of slider - r

Question

My shiny app looks like this:
library(shiny)
library(shinydashboard)
ui <- dashboardPage(
dashboardHeader(title = "Basic dashboard"),
dashboardSidebar(),
dashboardBody(
fluidRow(
box(plotOutput("plot1", height = 250)),
box(textInput("my_text", # supposed to be a numeric input
"Text input:"),
title = "Controls",
sliderInput("slider",
"Number of observations:",
min = 1, max = 100,
value = 50 # Want it to be output$my_init
)
)
)
)
)
server <- function(input, output) {
set.seed(122)
histdata <- rnorm(500)
output$plot1 <- renderPlot({
data <- histdata[seq_len(input$slider)]
hist(data)
})
# My attempt
# output$my_init <- input$my_text + 28
}
shinyApp(ui, server)
I want to set the initial value of the slider as output$my_init, a numeric variable that will be the result of operating some input variables. I tried using renderPrint, but the output is not numeric.
Thanks in advance.

Answer 1

I piggybacked on #stefan's comments and came up with this answer:
library(shiny)
library(shinydashboard)
ui <- dashboardPage(
dashboardHeader(title = "Basic dashboard"),
dashboardSidebar(),
dashboardBody(
fluidRow(
box(plotOutput("plot1", height = 250)),
box(numericInput("my_num", "Numeric input:", value = 50),
title = "Controls",
sliderInput("slider",
"Number of observations:",
min = 1, max = 100,
value = 50 # Want it to be output$my_init
)
)
)
)
)
server <- function(input, output) {
set.seed(122)
histdata <- rnorm(500)
output$plot1 <- renderPlot({
data <- histdata[seq_len(input$slider)]
hist(data)
})
# My attempt
observeEvent(input$my_num, {
updateSliderInput(inputId = "slider", value = input$my_num)
})
}
shinyApp(ui, server)
The idea is to use observeEvent() to trigger updateSliderInput() (update slider input widget) and update the value parameter of sliderInput()