title: How to find most common element in a list of list?
body: <p>I understand </p>
  
  <pre><code>a = max(set(lst), key=lst.count)
  </code></pre>
  
  <p>will derive most common element in a list </p>
  
  <p>but how do you derive most common element in a list of list without using helper function?</p>
  
  <p>For example </p>
  
  <pre><code>lst = [['1','2','3','4'],['1','1','1','1'],['1','2','3','4']]
  </code></pre>
  
  <p>The output should equal <code>1</code>.</p>
  
  <p>When I try <code>a = max(set(lst), key=lst.count)</code></p>
  
  <p>it writes <code>builtins.TypeError: unhashable type: 'list'</code></p>
  
  <p>Can anyone please help me?</p>