title: working with columns containing `call` class objects in `tidyr::unnest`
body: <p>I have a package that creates calls containing stats details that can then be displayed in plots.</p>
  
  <p>Here is a simple use case:</p>
  
  <pre class="lang-r prettyprint-override"><code># setup
  set.seed(123)
  library(statsExpressions)
  library(tidyverse)
  
  # two-sample t-test results in an expression
  stats_exp &lt;- bf_ttest(mtcars, am, wt)
  
  # class of object
  class(stats_exp)
  #&gt; [1] "call"
  
  # using the expression to display details in a plot
  ggplot(mtcars, aes(as.factor(am), wt)) + geom_boxplot() +
    labs(subtitle = stats_exp)
  </code></pre>
  
  <p><img src="https://i.imgur.com/81RgOKb.png" alt=""></p>
  
  <p>Now let's say I wanted to do the same kind of visualizations for all levels of a grouping variable.  In this case, I  will need to create and save the call for each level.</p>
  
  <p>I can successfully do so using <code>tidyr</code>, which can save the <code>call</code> objects in a list column:</p>
  
  <pre class="lang-r prettyprint-override"><code># doing this across groups
  (df &lt;- mtcars %&gt;%
    group_nest(cyl) %&gt;%
    mutate(stats_exp = data %&gt;% map(., ~bf_ttest(., am, wt))))
  
  # A tibble: 3 x 3
      cyl data               stats_exp 
    &lt;dbl&gt; &lt;list&gt;             &lt;list&gt;    
  1     4 &lt;tibble [11 × 10]&gt; &lt;language&gt;
  2     6 &lt;tibble [7 × 10]&gt;  &lt;language&gt;
  3     8 &lt;tibble [14 × 10]&gt; &lt;language&gt; 
  
  # did it work? yes!
  df$stats_exp[[1]]
  #&gt; atop(displaystyle(NULL), expr = paste("In favor of null: ", "log"["e"], 
  #&gt;     "(BF"["01"], ") = ", "-1.58", ", ", italic("r")["Cauchy"]^"JZS", 
  #&gt;     " = ", "0.71"))
  </code></pre>
  
  <p>The problem arises when I try to unnest it, which I would like to do since I will need to do some other operations on this dataframe somewhere downstream in my workflow:</p>
  
  <pre class="lang-r prettyprint-override"><code># unnest
  tidyr::unnest(data = df, cols = c(stats_exp, data)) 
  #&gt; Error: Input must be list of vectors
  </code></pre>
  
  <p>How can I avoid this error?</p>