Quantmod AddLines() Error: Object not found

Question

Recently I have been trying to use the addLines() function of quantmod along with Shiny package to overlay technical analysis vertical lines over the chartSeries. However, when I define global variables (followThroughDays and distributionDays in this case) and use them as arguments of the "v" parameter of addLines, an error message as follows appears:

object 'followThroughDays' not found

object 'distributionDays ' not found

 followThroughDays <- 2
 distributionDays <- 3

    output$plot <- 
        renderPlot({
          filtered_data <- window(stock_data, start = graph_start, end = state$progress)
          #flags <- getFollowThroughDaysRowNumber(filtered_data)
            switch(
                input$chartType, 
                "candle_stick" = chartSeries(filtered_data, TA=list(
                  "addLines(v=followThroughDays, on=-1, col='grey')",
                  "addLines(v=distributionDays, on=-1, col='orange')"
                )))})

What should I do so that the addLines argument can access the global variables for plotting the lines? The code works when I explicitly state the value (eg 2 or 3) stored in the variables but will show error messages when I used the variables as arguments directly.

Reproducible error download: https://drive.google.com/open?id=1ix81cd9gdJG6nXMM1v1WYwBE2nV0loPy

Answer 1

You've to overcome this error by using paste0 to create the TA argument value.

library("shiny")
library("ggplot2")
library("shinythemes")
library("lubridate")
library("quantmod")
library("data.table")

#source("dtstore.R")

fetchedStockData <- getSymbols("IBM", auto.assign = FALSE)

ui <- 
    fluidPage(
      plotOutput("plot")
        )

followThroughDays <- 300

server <- function(input, output, session) {
  TADays <- 3
  output$plot <- renderPlot({    
    chartSeries(fetchedStockData, theme = chartTheme("white"),
                type = "line", TA = paste0("addLines(v=",followThroughDays,", on=-1, col='orange')"))
  })
}

shinyApp(ui, server)