title: Drop rows based on column values in Dask
body: <p>I am using <code>dask</code> to read a large csv file. I wanted to drop a few rows based on one column value. If for that particular column the row value is empty I want to remove the entire row.</p>
  <p>I tried using <code>.dropna</code>:</p>
  <pre class="lang-py prettyprint-override"><code>df = df.dropna(subset=['tier1_name'],how = 'any',axis =0)
  </code></pre>
  <p>However, I got this error:</p>
  <pre><code>TypeError: dropna() got an unexpected keyword argument 'axis'
  </code></pre>
  <p>So I used <code>.drop</code> instead:</p>
  <pre class="lang-py prettyprint-override"><code>df.drop(df['tier1_name'].isnull(), axis = 0)
  </code></pre>
  <p>But then got this error:</p>
  <pre><code>&quot;Drop currently only works for axis=1 or when columns is not None&quot;
  NotImplementedError: Drop currently only works for axis=1 or when columns is not None
  </code></pre>
  <p>I don't understand what should I use to execute the desired operation. Help!</p>