title: R: predict new values for groups
body: <p>I've calculated a different regression for each group in a data frame:  </p>
  
  <pre><code>DF.L &lt;- DF %&gt;%
  group_by(Channel) %&gt;%
  do(Fit = rlm(L ~ -1 + Y + I(Y^2), data = .))
  </code></pre>
  
  <p>I want to apply this set of regressions to another data frame. To do so, I'm testing how to apply it to the same data frame:</p>
  
  <pre><code>DF %&gt;%
  group_by(Channel) %&gt;%
  do({
      Lfit &lt;- predict(subset(DF.L, Channel == unique(.$Channel))$Fit, .)
      data.frame(., Lfit)
  })
  glimpse(DF)
  </code></pre>
  
  <p>But I keep getting this error:</p>
  
  <pre><code>Error in UseMethod("predict") : 
    no applicable method for 'predict' applied to an object of class "list"
  Calls: %&gt;% ... do_.grouped_df -&gt; eval -&gt; eval -&gt; predict -&gt; predict
  </code></pre>
  
  <p>What I am doing wrong?</p>