How to check to see if a function is an object in the R workspace and if not, run a source file to i-CodePudding

In the below example code, the function testFunction() is defined in the separate source file functionsLibrary.R saved on the desktop. This example code works as intended.

How would I modify the code to first test if testFunction() is an object in the R workspace, and source it (running the line source("C:/Users/laran/OneDrive/Desktop/functionsLibrary.R")) only if the function is not in the workspace?

In the full code this is intended for, the function takes a very long time to run (reading a large data file into memory) and I only want it sourced if it is not currently a workspace object.

Example code:

library(shiny)

source("C:/Users/laran/OneDrive/Desktop/functionsLibrary.R")

ui <- fluidPage(
  br(),
  numericInput('selectValue','Select number of values to square:',value=1,step=1,min=1),
  br(),
  tableOutput('table')
)

server <- function(input,output,session)({
  output$table <- renderTable(testFunction(input$selectValue))
})

shinyApp(ui, server)

Source file contents (filename functionsLibrary.R):

testFunction <- function(a) {
  b <- data.frame(Value=seq(1:a),Square_Value = seq(1:a)^2)
  return(b)
}

CodePudding user response：

An easy way to go about this would be to use exist(). This should work for your problem.

library(shiny)

if (!exists("testFunction")) {
  source("C:/Users/laran/OneDrive/Desktop/functionsLibrary.R")
}

ui <- fluidPage(
  br(),
  numericInput('selectValue','Select number of values to square:',value=1,step=1,min=1),
  br(),
  tableOutput('table')
)

server <- function(input,output,session)({
  output$table <- renderTable(testFunction(input$selectValue))
})

shinyApp(ui, server)

We could extend the if clause to check if testFunction is really a function in case it exists and if not source the file.

if (!exists("testFunction") || (exists("testFunction") && !is.function(testFunction)))