Rcpp - how to call R function from Rcpp function in Shiny

Question

i just new with rcpp, i have a problem with my rcpp function, when i directly run App, the program display error could not find function "krit". but when i run the function partially with CTRL+R and then run App the program is running well. is there a code for call R function from rcpp function in shiny that i must not run the function partially? in other words, when i directly run App the shiny will running well. this is the example code...

server

library(shiny)
library(Rcpp)
krit <- function(n){
  mat <- matrix(1,n,1)
  return(mat)
}
cppFunction('
            NumericMatrix tes1(int n){
            Function krit("krit");
            NumericMatrix test = krit(n+1);
            return(test);
            }
            ')

shinyServer(function(input, output) {

  output$testing <- renderUI({
    list(
    renderPrint(tes1(3))
    )
  })

})

ui

library(shiny)
shinyUI(fluidPage(
  titlePanel("Shiny Text"),
  sidebarLayout(
    sidebarPanel(

    ),
    mainPanel(

      uiOutput("testing")
    )
  )
))

Possibly related to stackoverflow.com/questions/21225662/… — r2evans
– r2evans, Commented May 1, 2016 at 18:15
I put the code I need for our various shiny apps into packages which avoids the issue. — Dirk is no longer here
– Dirk is no longer here, Commented May 1, 2016 at 18:54

coatless · Accepted Answer · 2016-05-01 18:29:08Z

This is a scoping issue regarding how shiny and Rcpp view the different environments.

What's happening is an issue with accessing the global environment using...

1) Standard Rcpp::Function magic

Rcpp::Function krit("krit");

2) Rcpp::Environment with a global pull yields a missing value.

Rcpp::Environment env = Environment::global_env();
Rcpp::Function krit = env("krit");

Error:

file3d3f43b856e05.cpp:9:45: error: no match for call to '(Rcpp::Environment) (const char [5])'

Thus, the best that can be done to resolve this scoping issue is to pass the R function that you want to use into the compiled C++ function and call it. e.g.

NumericMatrix tes1(int n, Rcpp::Function krit)

Or, you will need to modify the server.R to:

library(shiny)
library(Rcpp)

krit <- function(n){
  mat <- matrix(1,n,1)
  return(mat)
}

cppFunction('
            // Added krit as a function pass
            NumericMatrix tes1(int n, Rcpp::Function krit){
            NumericMatrix test = krit(n+1);
            return(test);
            }
            ')

shinyServer(function(input, output) {

  output$testing <- renderUI({
    list(
      # Added parameter to `tes1` to pass in krit.
      renderPrint(tes1(n = 3, krit = krit))
    )
  })

})

Thus, you should get:

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