How to add a custom indicator to Shiny, R quantmod question

Question

I'm new with this trying to add a custom indicator to Shiny/R quantmod app.

The below code in R script works well.

library(quantmod)
getSymbols('SBUX')
barChart(SBUX)
# create new TA function
myInd <- function(x) {
  return(WMA(Cl(x)))
}
addMyInd <- newTA(FUN = myInd)
addMyInd()

The equivalent in shiny

library(shiny)
library(quantmod)

myInd <- function(x) {
  return(WMA(Cl(x)))
}
addMyInd <- newTA(FUN = myInd)

shinyServer(function(input, output,session) {
observe({
  query <- parseQueryString(session$clientData$url_search)
  dataInput <- reactive({ as.xts(getSymbols('SBUX', auto.assign = FALSE)) })
  output$chart <- renderPlot({ chartSeries(dataInput(), name = 'SBUX', TA = c(addMyInd()) ) })  
 })
})

fails with the Error: could not find function "myInd".

Whereas replacing "addMyInd" with any of the inbuilt function works well.

output$chart <- renderPlot({ chartSeries(dataInput(), name = 'SBUX', TA = c(addWMA()) )

Any idea how to make Shiny find the "myInd" function?

Answer 1

For anyone who might face a similar issue.

the trick is to put the two functions for the custom indicator inside another file and include it in server.R.

helper.R

library(quantmod)

myInd <- function(x) {
    return(WMA(Cl(x)))
}

addMyInd <- newTA(FUN = myInd)

and server.R just reads

library(shiny)
library(quantmod)

source("helper.R");

shinyServer(function(input, output,session) {
observe({
  query <- parseQueryString(session$clientData$url_search)
  dataInput <- reactive({ as.xts(getSymbols('SBUX', auto.assign = FALSE)) })
  output$chart <- renderPlot({ 
    chartSeries(dataInput(), name = 'SBUX', TA = c(addMyInd()) ) 
    }) 
 })
})