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

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")
)
)
))

Answer 1

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: