title: Change plot axis values dynamically from dataframe in Shiny
body: <p>I'm using Rstudio and Shiny for the project.</p>
  
  <p>I have defined a variable <code>res</code> and it contains dataframe with multiple rows and columns, then I make a plot and its x y and color are the data from <code>res</code> dataframe.
  My problem is that when i Run it, if I write that i want x axis to be inputted variable values (<code>input$SelInp</code>), I dont get dataframe values, instead, I get only column name. </p>
  
  <p>if I change the code to get the values directly from dataframe (<code>res$some_column_name</code>) I get the correct values.</p>
  
  <p>ui.R</p>
  
  <pre><code>selectInput("SelInp",
                           label = "Choose one:",
                           choices = colnames(res)
                           )
  </code></pre>
  
  <p>server.R</p>
  
  <pre><code>  output$plt = renderPlot({
                    qplot(data = res,
                       x = input$SelInp, #this only returns a column name 
                       y = res$loan_amnt, # this returns correct values from column loan_amt
                       ylab = "some y axis",
                       xlab = "some x axis",
                       main="Our Chart")
                       }
                       )
  </code></pre>
  
  <p>so, I want to get the values in <code>input$SelInp</code> thanks in advance</p>