title: How to count the number of times a sequence of columns appears in a data frame?
body: <p>I have this dataframe <code>df</code>:</p>
  
  <pre><code>AA_0    AA_1     AA_2     AA_3
  store   cake     mass     visit    
  store   mass     visit
  mass    store
  store   cake     mass     visit
  </code></pre>
  
  <p>I want to calculate the number of times each that each sequence <code>AA_0</code>-<code>AA_3</code> appears in <code>df</code> and represent the result as follows:</p>
  
  <pre><code>result = 
  
      count   data
      2       store/cake/mass/visit
      1       store/mass/visit
      1       mass/store
  </code></pre>
  
  <p>How can I do it?</p>