title: Python list, keep all value present in all sublist of a list
body: <p>I need to find all value that are present in all sublist of a larger list (they are all ids)</p>
  
  <p>What I have tried is first getting all uniques values present in all list and they test each value but this is extremly slow on a big list</p>
  
  <pre class="lang-py prettyprint-override"><code>l1 = ["a", "b", "c", "d", "e", "f"]
  l2 = ["b", "c", "e", "f", "g"]
  l3 = [ "b", "c", "d", "e", "f", "h"]
  LL = [l1, l2, l3]
  LL
  unique_ids = set(x for l in LL for x in l)
  
  filter_id = []
  lenList = len(LL)
  for id in unique_ids:
      if sum(id in item for item in LL) == lenList:
          filter_id.append(id)
  </code></pre>
  
  <p>How could I speed up the search ?</p>