title: t test by using R studio:grouping factor must have exactly 2 levels error
body: <p><img src="https://i.stack.imgur.com/TqNYf.jpg" alt="enter image description here"></p>
  
  <p>I don't speak English well.
  I am doing t test by using R studio, but I have a big problem.</p>
  
  <p>error :grouping factor must have exactly 2 levels</p>
  
  <p><img src="https://i.stack.imgur.com/lAI2W.jpg" alt="enter image description here"></p>
  
  <p>This data picture doesn't have all data, but value1 column have o ,x, NA. 
  how can I solve this problem.</p>