Object Not found error in my Shiny server.R code - r

Question

I am new to R programming. When I execute my shiny app code, I get the error "Error in func() : object 'file3' not found". Any suggestions on how to resolve this? Below is the server.R code where I have the error:
library(shiny)
shinyServer(function(input, output) {
reactive ({
if(is.null(input$file1)) return(NULL)
fl1 <- paste("file:///",input$file1,sep='')
if(is.null(input$file2)) return(NULL)
fl2 <- paste("file:///",input$file2,sep='')
file1 <- read.table(fl1,sep=',',header=TRUE)
file2 <- read.table(fl2,sep=',',header=TRUE)
library(sqldf)
options(gsubfn.engine = "R")
file3 <- sqldf('SELECT * FROM file2 UNION ALL SELECT * FROM file1')
})
output$text1 <- renderTable({ file3 })
})

Answer 1

I am answering based on the code provided, since you reference input$xx, I assume that you have a ui.R file :-). Also if your files are uploaded files you will need to handle them using shiny::observeEvent, otherwise input$file1 and input$file2 will always be NULL.
You also should ensure that the UI object with inputID = "text1" is defined as a dataTable output rather than a textOutput. So something like this: shiny::dataTableOutput("text1"). This will ensure that your input is parsed correctly.
I have also fixed some of your styling to make you code more readable. See google R Style Guide.
You can try the following, taking into account the above:
library(shiny)
library(sqldf)
options(gsubfn.engine = "R")
shinyServer(function(input, output) {
getData <- reactive ({
if(is.null(input$file1)) return(NULL)
fl1 <- paste("file:///", input$file1, sep = '')
if(is.null(input$file2)) return(NULL)
fl2 <- paste("file:///", input$file2, sep='')
file1 <- read.table(fl1, sep = ',', header = TRUE)
file2 <- read.table(fl2, sep = ',', header = TRUE)
file3 <- sqldf('SELECT * FROM file2 UNION ALL SELECT * FROM file1')
return(file3)
})
output$text1 <- shiny::renderDataTable({ getData() })
})
I hope this helps. You may also want to try using DT::renderDataTable instead of shiny::renderDataTable