title: How to mutate variable with tidyevaluation
body: <p>I'm trying to create a function that prints a plot when user inputs data and variables what to plot. My current problem is that group/subgroup columns may be numeric so I need to mutate them into factors before plotting. I'm trying to do it with this:</p>
  <pre><code>create_plot &lt;- function(df, group, subgroup, y){
    df %&gt;% 
      select({{group}}, {{subgroup}}, {{y}}) %&gt;% 
      mutate({{group}} = as.factor({{group}})) %&gt;% 
      ggplot() +
      geom_boxplot(aes(x={{subgroup}}, y={{y}}, color={{group}}))
    }
  
  create_plot(sales, YEAR, COUNTRY, VALUE)
  </code></pre>
  <p>But it gives an error:</p>
  <pre><code>Error: unexpected '=' in:
  &quot;    select({{group}}, {{subgroup}}, {{y}}) %&gt;% 
      mutate({{group}} =&quot;
  </code></pre>
  <p>Which leads me to believe mutate shouldn't be used with {{variables}}. How to do this correctly?</p>