title: pandas - filter dataframe by another dataframe by row elements
body: <p>I have a dataframe <code>df1</code> which looks like:</p>
  <pre><code>   c  k  l
  0  A  1  a
  1  A  2  b
  2  B  2  a
  3  C  2  a
  4  C  2  d
  </code></pre>
  <p>and another called <code>df2</code> like:</p>
  <pre><code>   c  l
  0  A  b
  1  C  a
  </code></pre>
  <p>I would like to filter <code>df1</code> keeping only the values that ARE NOT in <code>df2</code>. Values to filter are expected to be as <code>(A,b)</code> and <code>(C,a)</code> tuples. So far I tried to apply the <code>isin</code> method:</p>
  <pre><code>d = df[~(df['l'].isin(dfc['l']) &amp; df['c'].isin(dfc['c']))]
  </code></pre>
  <p>That seems to me too complicated, it returns:</p>
  <pre><code>   c  k  l
  2  B  2  a
  4  C  2  d
  </code></pre>
  <p>but I'm expecting:</p>
  <pre><code>   c  k  l
  0  A  1  a
  2  B  2  a
  4  C  2  d
  </code></pre>