title: Multiplying 2 pandas dataframes generates nan
body: <p>I have 2 dataframes as below</p>
  <pre><code>import pandas as pd
  dat = pd.DataFrame({'val1' : [1,2,1,2,4], 'val2' : [1,2,1,2,4]})
  dat1 = pd.DataFrame({'val3' : [1,2,1,2,4]})
  </code></pre>
  <p>Now with each column of <code>dat</code> and want to multiply <code>dat1</code>. So I did below</p>
  <pre><code>dat * dat1
  </code></pre>
  <p>However this generates <code>nan</code> value for all elements.</p>
  <p>Could you please help on what is the correct approach? I could run a <code>for</code> loop with each column of dat, but I wonder if there are any better method available to perform the same.</p>
  <p>Thanks for your pointer.</p>