擅长:python、mysql、java
<p>用一条带<code>reindex</code>的线链做</p>
<pre><code>dfb.groupby(['id', 'value'])['count'].sum().\
unstack(fill_value=0).\
reindex(columns=dfa.columns,index=dfa.id,fill_value=0).\
drop('id',1)
groupA groupB groupC groupD groupE
id
1 2 3 1 0 0
2 1 1 0 0 0
3 0 0 2 0 0
</code></pre>