title: Error: non-numeric argument to binary operator
body: <p>Good Day, making application in RStudio/Shiny is very new to me and I am working with a project in  which an external file is to be used as the input data. Here is my CSV: <img src="https://i.stack.imgur.com/AGPNu.jpg" alt="Click to see: Wattage of an Appliance" /></p>
  <p>my supposed to be app:</p>
  <p><img src="https://i.stack.imgur.com/3tEwK.jpg" alt="Click to see: calculator to compute electric bill" /></p>
  <p>So the user insert a csv with appliance name in row 1 and their wattage in row 2 just like in the picture above, then the selectInput will be updated. The user choose what appliance and hours of usage then it will be calculated for its cost</p>
  <p>Here is my server code:</p>
  <pre><code>server &lt;- function(input,output,session) {
    
    observeEvent(input$file1, {
      
      mytable &lt;- read.csv(input$file1$datapath)
      
      updateSelectInput(session, &quot;select&quot;, &quot;Appliances&quot;, 
                        choices = colnames(mytable))
      
    })
    
    dataset_day &lt;- reactive ({
      costday &lt;- ((input$select * input$hour) / 1000) * 8.9535
      costday &lt;- data.frame(costday)
      names(costday)  &lt;- &quot;Electricity Cost per day (Philippine Peso)&quot;
      print(costday)
    })
    
    dataset_month &lt;- reactive ({
      costmonth &lt;- (((input$select * input$hour) / 1000) * 8.9535) * 30
      costmonth &lt;- data.frame(costmonth)
      names(costmonth)  &lt;- &quot;Electricity Cost per month (Philippine Peso)&quot;
      print(costmonth)
    })
  </code></pre>
  <p>I need help in putting the value written in the CSV of the chosen appliance by the user to the equation.</p>
  <p>In short how to fix the non-numeric argument to binary operator error.</p>
  <p>I think the error is in the input$select but I am lost about this.</p>
  <pre><code>((input$select * input$hour) / 1000) * 8.9535
  </code></pre>
  <p>Do I need to change or add something in order to fix this? Is this app possible to do? Thank you in advance!</p>