title: check and create not exist variables in r
body: <p>Case by case, variables are existed 'group1' or 'group1', 'group2' or 'group1', group2' 'group3' (these are variable).</p>
  
  <p>However, I want to make three group variables every time.</p>
  
  <p>For example, if I have only one group variable 'group1', but I want to get 'group1', 'group2', and 'group3' ('group2' and 'group3' will be empty column).</p>
  
  <p><a href="https://i.stack.imgur.com/s2csX.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/s2csX.jpg" alt="enter image description here"></a></p>
  
  <p>I think it will work checking the variable name and making not exists variables.</p>
  
  <p>Let me know how can I work this.</p>