title: Find element in a list
body: <p>I have this character vector:</p>
  
  <pre><code>fruits &lt;- c("melon", "grapefruit", "blueberry")
  </code></pre>
  
  <p>I also have this list:</p>
  
  <pre><code>list_fruits &lt;- list(list(first = "orange", second =  NULL,  third = "pineapple"),
                 list(first = "apple",  second = NULL, third = "melon"))
  
  list_fruits
  
  [[1]]
  [[1]]$first
  [1] "apple"
  
  [[1]]$second
  NULL
  
  [[1]]$third
  [1] "pineapple"
  
  
  [[2]]
  [[2]]$first
  [1] "apple"
  
  [[2]]$second
  NULL
  
  [[2]]$third
  [1] "melon"
  </code></pre>
  
  <p>If any element of <code>fruits</code> is equal to the element any list <code>third</code> in <code>list_fruits</code>, I need the list <code>first</code> of <code>list_fruits</code> to be outputed as a character vector. </p>
  
  <p>So if I ran the function on <code>list_fruits</code>, the output would be:</p>
  
  <pre><code>"apple"
  </code></pre>