title: Multiplying pandas dataframe and series, element wise
body: <p>Lets say I have a pandas series:</p>
  
  <pre><code>import pandas as pd
  x = pd.DataFrame({0: [1,2,3], 1: [4,5,6], 2: [7,8,9] })
  y = pd.Series([-1, 1, -1])
  </code></pre>
  
  <p>I want to multiply x and y in such a way that I get z:</p>
  
  <pre><code>z = pd.DataFrame({0: [-1,2,-3], 1: [-4,5,-6], 2: [-7,8,-9] })
  </code></pre>
  
  <p>In other words, if element j of the series is -1, then all elements of the j-th row of x get multiplied by -1. If element k of the series is 1, then all elements of the j-th row of x get multiplied by 1. </p>
  
  <p>How do I do this?</p>