title: Drop rows based on column value (Dask)
body: <p>I want to drop certain rows of a Dask DataFrame based on the value of a column.</p>
  <p>I've had no problems in the past doing this:</p>
  <pre><code>ddf = ddf[ (ddf['col'] == str1) | (ddf['col'] == str2)]
  </code></pre>
  <p>What I have now is a little different.
  This column contains a string like 'abc,def,ghk' and I want to drop it if it doesn't contain 'abc' or 'doh'.</p>
  <p>I've tried stuff like:</p>
  <pre><code> ddf = ddf[ ('abc' in ddf['col']) | ('doh' in ddf['col'])]
  </code></pre>
  <p>But I get</p>
  <pre><code> KeyError: True
  </code></pre>
  <p>(I think) because the expression returns a bool and there's no key with that value,</p>
  <p>And</p>
  <pre><code> ddf = ddf.drop(ddf.index[('abc' in ddf['col']) | ('doh' in ddf['col'])])
  </code></pre>
  <p>which gives me</p>
  <pre><code> NotImplementedError: Series getitem in only supported for other series objects with matching partition structure
  </code></pre>
  <p>What am I doing wrong?</p>