title: How to subtract rows of one pandas data frame from another?
body: <p>The operation that I want to do is similar to merger. For example, with the <code>inner</code> merger we get a data frame that contains rows that are present in the first AND second data frame. With the <code>outer</code> merger we get a data frame that are present EITHER in the first OR in the second data frame.</p>
  
  <p>What I need is a data frame that contains rows that are present in the first data frame AND NOT present in the second one? Is there a fast and elegant way to do it?</p>