title: Fuzzyjoin left_join on two columns
body: <p>I have two datasets I want to join in a Shiny application</p>
  
  <p>Both have two columns- dates and alphanumeric strings that the user chooses</p>
  
  <p>eg The format of the columns is the same in the two dataframes ie:</p>
  
  <pre><code>EndoNum   EndoDate         PathNum   PathDate        
  F321321  13/12/2001       F321321  21/12/2001
  </code></pre>
  
  <p>I want to left join dataset one with dataset two but the dates are out by between 1-8 days</p>
  
  <p>I have tried from <code>fuzzyjoin</code>:</p>
  
  <pre><code>        EndoDate&lt;-colnames(RV$data[as.numeric(input$endotable_columns_selected[1])])
          EndoNum&lt;-colnames(RV$data[as.numeric(input$endotable_columns_selected[2])])
          PathDate&lt;-colnames(RV2$data[as.numeric(input$endotable_columns_selected[1])])
          PathNum&lt;-colnames(RV2$data[as.numeric(input$endotable_columns_selected[2])])
  
  
    difference_left_join(RV2$data,
                            RV$data,
                            by=setNames(nm=c(EndoNum,EndoDate),c(PathNum,PathDate)),
                            max_dist = 8,
                            distance_col = "Days"
       )
  </code></pre>
  
  <p>but I get the error: <code>Error in v1 - v2 : non-numeric argument to binary operator</code></p>
  
  <p>How can I make the join. Do I have to use fuzzyjoin?</p>