[Defuse Shiny Reactives] Useful R Code Displaying How to "Defuse" Reactives into Static Values #dev #shiny #pinned

defuse_shiny_reactives.R

code <- 
  "library(shiny)
  library(dplyr)
  library(ggplot2)
  input <- list(cty = 15)
  
  df = shiny::reactive({
    x <- input$cty
    mpg %>% filter(cty < x)
  })
  
  this_is_crazy <- shiny::reactive
  
  n_obs <- reactive(nrow(df()))
  df_head <- this_is_crazy(head(df()))"

# or if code is in a script use code <- file(<path>)

is_assigned_reactive <- function(expr) {
  # discard obvious
  if (
    rlang::is_symbol(expr) ||
    !(expr[[1]] == "<-" || expr[[1]] == "=") ||
    length(expr) != 3
  ) {
    return(FALSE)
  }
  
  fn_expr <- expr[[3]][[1]]
  
  # Check that it's actually `shiny::reactive` being called
  identical(rlang::eval_bare(fn_expr), shiny::reactive)
}

replace_reactive_expr <- function(expr) {
  if (length(expr) > 1) {
    # recurse all the way into the parsed code tree
    lapply(expr, replace_reactive_expr)
  }
  # on the way back up, catch any assigned reactives
  if (is_assigned_reactive(expr)) {
    # and replace the reactive with a function
    expr[[3]] <- rlang::new_function(NULL, expr[[3]][[2]])
  }
  expr
}

eval_with_defused_reactive <- function(code, envir = globalenv()) {
  # parse the code, then evaluate each expression after replacing reactives
  exprs <- rlang::parse_exprs(code)
  for (expr in exprs) {
    eval(replace_reactive_expr(expr), envir = envir)
  }
}

eval_with_defused_reactive(code)

df()
n_obs()
df_head()

test_script.R

library(shiny)
library(dplyr)
library(ggplot2)

input <- list(cty = 15)
  
df <- shiny::reactive({
  x <- input$cty
  mpg %>% filter(cty < x)
})
  
this_is_crazy <- shiny::reactive
  
n_obs <- reactive(nrow(df()))
df_head <- this_is_crazy(head(df()))