How can we use `names()` or an alternative to name `reactiveVal` inside Shiny app?

I tried to use names() on a reactiveVal inside a shiny app without success.

Is this even possible? What are alternative ways to name reactive values in shiny apps?

My first attempt throws an error:

names(r()) <- "something"

Error in names(r()) <- "something" : invalid (NULL) left side of assignment

My second attempt as well:

names(r) <- "something"

Error in names(r) <- "something" : names() applied to a non-vector

Here is a minimal example app:

library(shiny)

ui <- fluidPage(mainPanel(textOutput("text")))

server <- function(input, output) {
  r <- reactiveVal(1)
  # names(r) <- "something"
  output$text <- renderText(
    paste0("The reactiveVal is ", r(),". It's name is ", names(r()),"."))
}

shinyApp(ui = ui, server = server)

Solution

The key is in the documentation on how to set values. From the docs:

Call the function with no arguments to (reactively) read the value; call the function with a single argument to set the value.

This means it gets a little bit esoteric and I personally prefer to use magrittr aliases and a pipe to keep things readable. The key steps for setting the names of your reactive value later on are:

call it with no arguments r(), to read the current value.
wrap the call in isolate to prevent any reactivity on this step
pass the returned value to set_names along with the name string.
call the reactive value r again with the named value as an argument, to set r.

library(shiny)
library(magrittr)
ui <- fluidPage(mainPanel(textOutput("text")))

server <- function(input, output) {
  r <- reactiveVal(1 %>% set_names("something")) #setting the name on initial

  isolate(r()) %>% 
    set_names("something else") %>%  
    r()
  output$text <- renderText(
    paste0("The reactiveVal is ", r(),". It's name is ", names(r()),"."))
}

shinyApp(ui = ui, server = server)
#> PhantomJS not found. You can install it with webshot::install_phantomjs(). If it is installed, please make sure the phantomjs executable can be found via the PATH variable.

Shiny applications not supported in static R Markdown documents

^{Created on 2019-08-07 by the reprex package (v0.3.0)}