title: Pandas join DataFrame and Series over a column
body: <p>I have a Pandas DataFrame <code>df</code> that store a matching between a label and an integer, and a Pandas Series <code>s</code> that contains a sequence of labels : </p>
  
  <pre><code>print(df)
  
            label    id
  0     AAAAAAAAA     0
  1     BBBBBBBBB     1
  2     CCCCCCCCC     2
  3     DDDDDDDDD     3
  4     EEEEEEEEE     4
  
  
  print(s)
  
  0        AAAAAAAAA
  1        BBBBBBBBB
  2        CCCCCCCCC
  3        CCCCCCCCC
  4        EEEEEEEEE
  5        EEEEEEEEE
  6        DDDDDDDDD
  </code></pre>
  
  <p>I want to join this DataFrame and this Series, to get the sequence of integer corresponding to my sequence <code>s</code>.
  Here is the expected result of my example : </p>
  
  <pre><code>print(df.join(s)["id"])
  
  0        0
  1        1
  2        2
  3        2
  4        4
  5        4
  6        3
  </code></pre>