title: How to specify offset using `@formula` and implement a similar function to `model.frame()` in R using Julia?
body: <p>Given the model formula, response family and DataFrame, I would like to return as the output of this function things such as <code>n</code>, <code>p</code>, <code>model_matrix</code>, <code>model_response</code>, <code>model_offset</code>. Offsets are very important for our use case but I cannot work out how to specify a formula within Julia accounting for offset terms.</p>
  <pre><code>function frame(formula,family,data)
      # code to implement something similar to `model.frame` function in R
  
     return model_matrix,model_response,model_response
  end
  </code></pre>