Warning: Error in [[.shinyoutput: Reading from shinyoutput object is not allowed - r

Question

I have a function which I'd like to handle multiple outputs but base it off of the input to the function. For example, in the following code side could refer to any number of maps on the page, e.g. 10:
library(shiny)
ui <- fluidPage(
textOutput("m1"),
textOutput("m2")
)
f <- function(output, side) {
m = output[[paste0('m', side)]]
print(m)
}
server <- function(input, output, session) {
f(output, 1)
f(output, 2)
}
shinyApp(ui, server)
However, running this code results in the following error:
Warning: Error in [[.shinyoutput: Reading from shinyoutput object is not allowed.

Answer 1

You have to create a reactive context for each output. This would be the first solution of doing it. This way you write a function that creates a renderText output in each call.
library(shiny)
ui <- fluidPage(
textInput("in1", "Value"),
textOutput("m1"),
textOutput("m2")
)
server <- function(input, output, session) {
f <- function(outputId, side) {
output[[outputId]] <<- renderText({
paste0('m', side, " - ", input$in1)
})
}
f("m1", 1)
f("m2", 2)
}
shinyApp(ui, server)
The solution above duplicates code. For most apps that shouldn't be a problem. But if you need to avoid that:
library(shiny)
ui <- fluidPage(
textInput("in1", "Value"),
textOutput("m1"),
textOutput("m2")
)
server <- function(input, output, session) {
f <- function(outputId, side) {
paste0('m', side, " - ", input$in1)
}
output$m1 <- renderText({
f("m1", 1)
})
output$m2 <- renderText({
f("m2", 2)
})
}