R - error “non-numeric argument to binary operator” in shiny

Question

I'm very new to r (and programming in general) and we were asked to make a web app using r shiny, the plan was to make a matrix operations calculator from different input files,(first.cvs file contains matrix 1, 2nd.cvs file contains matrix 2) but an error keeps appearing

 Listening on http://127.0.0.1:3420
 Warning: Error in FUN: non-numeric argument to binary operator
 99: eval
 98: eval
 97: Ops.data.frame
 96: renderTable [C:/Users/Acer/Desktop/FirstWebApp/app (1).R#45]
 95: func
 82: origRenderFunc
 81: output$oput
  1: runApp

this is my UI

     ui <- fluidPage(
  titlePanel("Multiple file uploads"),
  sidebarLayout(
    sidebarPanel(
     fileInput("file1",
               label="Upload CSVs here"),
     fileInput("file2", "upload file here"),
     selectInput("ops", "Select Operation",
                 choices = c("addition","subtraction","multiplication","division"))
     
  ),
  mainPanel(
     tableOutput("input_file"),
     tableOutput("input_file2"),
     tableOutput("oput")

and my server looks like this

server <- function(input, output) {
output$input_file <- renderTable({
  file_to_read =  input$file1
  if (is.null(file_to_read)) {
    return()
 }
  read.table(file_to_read$datapath, sep = ',', header = FALSE)
})

output$input_file2 <- renderTable({
  file_to_read =  input$file2
  if (is.null(file_to_read)) {
    return()
  }
  read.table(file_to_read$datapath, sep = ',', header = FALSE)
})
output$oput <- renderTable({
switch(input$ops,
       "addtion" = input$file1 + input$file2,
       "subtraction" = input$file1 - input$file2,
       "multiplication" = input$file1 * input$file2,
       "division" = input$file1 / input$file2)
})
}

how do I fix this and if this error is fixed will the program run?

Answer 1

Your Ui is good no need to change anything. But your server code has minor corrections. Problem lies in your switch case:

switch(input$ops,
       "addtion" = input$file1 + input$file2,
       "subtraction" = input$file1 - input$file2,
       "multiplication" = input$file1 * input$file2,
       "division" = input$file1 / input$file2)
})

here you are adding input$file1 & input$file2. input$file1 is not a matrix of your data, but it is a dataframe of:

Browse[1]> input$file1
       name size     type
1 file1.csv   21 text/csv
                                                                          datapath
1 C:\\Users\\temp\\AppData\\Local\\Temp\\RtmpCEZJPF/957a518de2fae08f6a7b7201/0.csv

Therefore you have to store your matrix data in a reactiveVal() for using them later in the switch case

server <- function(input, output) {
  
  file1_Result <- reactiveVal(NULL)
  file2_Result <- reactiveVal(NULL)
  
  
  output$input_file <- renderTable({
    file_to_read =  input$file1
    if (is.null(file_to_read)) {
      return()
    }
   Result <- read.table(file_to_read$datapath, sep = ',', header = FALSE)
   file1_Result(Result)
   return(Result)
  })
  
  output$input_file2 <- renderTable({
    file_to_read =  input$file2
    if (is.null(file_to_read)) {
      return()
    }
    Result <- read.table(file_to_read$datapath, sep = ',', header = FALSE)
    file2_Result(Result)
    return(Result)
  })
  output$oput <- renderTable({
    browser()
    switch(input$ops,
           "addtion" = file1_Result() + file2_Result(),
           "subtraction" = file1_Result() - file2_Result(),
           "multiplication" = file1_Result() * file2_Result(),
           "division" = file1_Result() / file2_Result())
  })
}

Hope this works:-)