title: Group by a column of comma delimited strings, but grouping should ignore specific order of strings
body: <p>Let's say I have the following data</p>
  
  <pre><code>&gt; summary_table[, c('condition_list', 'condition_count')]
  # A tibble: 4,306 x 2
     condition_list             condition_count
     &lt;chr&gt;                                &lt;int&gt;
   1 true control,control email               2
   2 true control,control email               1
   3 treatment, control email                 1
   4 true control, control email              1
   5 control email, true control              1
   6 control email                            1
   7 control email, treatment                 1
   8 control email,true control               2
   9 treatment                                1
  10 control email, true control              1
  </code></pre>
  
  <p>Notice that  the column "condition_list" consists of comma-limited strings indicating an assignment to some condition, but some of these assignments are isomorphic to each other.  I'd like to get a tally of the number of rows in each condition like so:</p>
  
  <pre><code>summary_table %&gt;% group_by(condition_list) %&gt;%
    summarize(n= n())
  </code></pre>
  
  <p>However, this will treat each specific combination of <code>condition_list</code> as a separate group.  I want it to treat "control email, true control" the same as "true control, control email."  What is the best way to do this?</p>
  
  <pre><code>&gt; dput(dputter)
  structure(list(condition_list = c("true control,control email", 
  "true control", "treatment", "true control", "control email", 
  "control email", "control email", "control email,true control", 
  "treatment", "control email", "true control,treatment", "treatment,true control", 
  "treatment,true control,control email", "control email", "treatment", 
  "true control,control email", "control email", "treatment", "true control,treatment", 
  "control email", "control email,true control", "treatment", "control email", 
  "control email", "control email,true control", "control email", 
  "control email", "true control", "treatment", "true control", 
  "treatment", "true control", "true control", "control email", 
  "true control", "control email", "control email", "true control", 
  "treatment", "treatment,true control,control email", "true control", 
  "true control", "treatment,control email", "true control", "true control", 
  "control email", "control email", "treatment", "control email", 
  "true control"), condition_count = c(2L, 1L, 1L, 1L, 1L, 1L, 
  1L, 2L, 1L, 1L, 2L, 2L, 3L, 1L, 1L, 2L, 1L, 1L, 2L, 1L, 2L, 1L, 
  1L, 1L, 2L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 
  1L, 3L, 1L, 1L, 2L, 1L, 1L, 1L, 1L, 1L, 1L, 1L)), class = c("tbl_df", 
  "tbl", "data.frame"), row.names = c(NA, -50L))
  </code></pre>