basic groupby operations in Dask
<p>I am attempting to use Dask to handle a large file (50 gb). Typically, I would load it in memory and use Pandas. I want to groupby two columns "A", and "B", and whenever column "C" starts with a value, I want to repeat that value in that column for that particular group.</p>

<p>In pandas, I would do the following:</p>

<pre><code>df['C'] = df.groupby(['A','B'])['C'].fillna(method = 'ffill')
</code></pre>

<p>What would be the equivalent in Dask? 
Also, I am a little bit lost as to how to structure problems in Dask as opposed to in Pandas,</p>

<p>thank you,</p>

<p>My progress so far:</p>

<p>First set index:</p>

<pre><code>df1 = df.set_index(['A','B'])
</code></pre>

<p>Then groupby:</p>

<pre><code>df1.groupby(['A','B']).apply(lambda x: x.fillna(method='ffill').compute()
</code></pre>