title: Pandas: return dataframe where one column's values are greater than another
body: <p>Apologies if this is a duplicate but I can't seem to find a working example in the pandas docs, SO or google.</p>
  
  <p>How do you return a dataframe where the values of one column are greater than the values of another?</p>
  
  <p>Should be something like this: <code>df['A'].where(df['A']&gt;df['B'])</code></p>
  
  <p>But this returns only a vector. I need the full filtered dataframe. </p>