R, vector of strings to vector of inputs - r

Question

TL;DR:
I have this vector/list of characters, it could either look like this:
list_of_inputs <- c('input$thing_1', 'input$thing_2', ...)
or like this:
list_of_inputs <- c('thing_1', 'thing_2', ...)
What I need is to convert it so it is interpreted like this:
c(input$thing_1, input$thing_2, ...)
Is this possible?
The reason is I want to programatically make shiny inputs, and programatically check when one of them has been hit. If I manually declare inputs in ui.R/ui-function, this works:
observeEvent(c(input$manually_made_1, input$manually_made_2), {
print('a button has been hit!')
}
And this also works:
observeEvent(c(input[['manually_made_1']], input[['manually_made_2']]), {
print('a button has been hit!')
}
I can't just give observeEvent the list_of_inputs as a vector/list of strings/characters, as it doesn't understand that. But if I try to make a list using a loop:
input_list <- c()
for(i in 1:length(list_of_inputs){
input_list <- append(input_list, input[[paste0('thing_',i)]])
}
input_list ends up containing nothing but NULL (or several)...
I tried using as.symbol() but that didn't seem to work. Any suggestions?

Answer 1

Here is an alternate solution for your consideration. The Shiny app below takes a list of lists of button information (id, label, and callback) and adds an actionButton and observer for each item. Each button press will trigger the corresponding callback function from the list.
The call to local() is key. If the call to local is removed only the final expression of the for loop is registered as an observer. Credit for the local workaround goes to this thread https://gist.github.com/wch/5436415/ and Winston Chang.
If multiple buttons need to share a callback you can define the function outside of the list and reference it multiple times. If there is no need for multiple callbacks you could forgo including a callback element in the lists and build out the event expression of observeEvent instead.
library(shiny)
myButtons <- list(
list(
id = "first",
label = "First Button",
callback = function() {
print("The first button was pushed??")
}
),
list(
id = "second",
label = "Second Button",
callback = function() {
print("And now the second button was pushed")
}
)
)
shinyApp(
ui = fluidPage(
lapply(
myButtons,
function(btn) actionButton(btn$id, btn$label)
)
),
server = function(input, output, session) {
for (btn in myButtons) {
local({
btnLocal <- btn
observeEvent(input[[btnLocal$id]], {
btnLocal$callback()
})
})
}
}
)