title: How to get the frequency of items in a list with the different length
body: <p>Suppose I have the following list:</p>
  
  <pre><code>test&lt;-list(c("a","b","c"),c("a"),c("c"))
  &gt;test
  [[1]]
  [1] "a" "b" "c"
  
  [[2]]
  [1] "a"
  
  [[3]]
  [1] "c"
  </code></pre>
  
  <p>What do I do(or functions to use) to get the frequency of unique items in a list like this:?</p>
  
  <pre><code>a 2
  b 1
  c 2
  </code></pre>
  
  <p>I tried using table(test), but I get the following error</p>
  
  <pre><code>&gt; table(test)
  Error in table(test) : all arguments must have the same length
  </code></pre>