title: How to use a Pandas series as a lookup for another series
body: <p>For two series: one with numeric identifiers and another that is a lookup associating those identifiers to names, how can I join them?  Example:</p>
  
  <p><strong>Series with numeric IDs</strong>:</p>
  
  <pre><code>data_series = pd.Series(np.random.randint(0,100,5),
                          index = ["id_"+i for i in np.arange(5).astype('str')])
  print(data_series)
  
  id_0    38
  id_1    35
  id_2    36
  id_3    32
  id_4    94
  dtype: int64
  </code></pre>
  
  <p><strong>Series with names to look up:</strong></p>
  
  <pre><code>name_lookup_series = pd.Series(['Google','YouTube','Facebook','Baidu','Wikipedia'],
                          index=["id_"+i for i in np.arange(5).astype('str')])
  print(name_lookup_series)
  
  id_0       Google
  id_1      YouTube
  id_2     Facebook
  id_3        Baidu
  id_4    Wikipedia
  dtype: object
  </code></pre>
  
  <p><strong>Desired data frame</strong>:</p>
  
  <pre><code>Google       38
  YouTube      35
  Facebook     36
  Baidu        32
  Wikipedia    94
  dtype: int64
  </code></pre>
  
  <p>I am able to do this by hacking away with Pandas-fu, but this such a common <code>join</code>-looking operation I assume there is a more idiomatic way to do it.  My current method:</p>
  
  <pre><code>data_series.index = data_series.index.map(lambda x: name_lookup_series.loc[x])
  </code></pre>
  
  <p>Is there another way to do this, preferably with cleaner code and in one line?</p>