title: Selecting multiple index values in a pandas series
body: <p>Suppose I have a Pandas Series:</p>
  
  <pre><code>import pandas as pd
  foo = pd.Series(data=[1,2,3], index=['a','b','c'])
  foo
  
  a    1
  b    2
  c    3
  dtype: int64
  </code></pre>
  
  <p>Comparing the index to a value returns a nice selector array:</p>
  
  <pre><code>foo.index == 'c'
  
  array([False, False,  True], dtype=bool)
  </code></pre>
  
  <p>What is the expression for a selector array for 'a' and 'c' ([True, False, True])?</p>
  
  <p>Not this:</p>
  
  <pre><code>foo.index in ['a', 'c']
  
  ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()
  </code></pre>
  
  <p>This is a simple example, but the true one is more complicated, and I want to select 10 or 15 items, so I'd like a concise format, ideally listing the elements I want to select by name.</p>
  
  <p>I'm using pandas 0.23.4.</p>