擅长:python、mysql、java
<p>这将完成以下工作:</p>
<pre><code>df = pd.DataFrame(dict(a=[0,1], b=[3,4], c=[6,7]),
index=['spam', 'ham'])
mask = pd.DataFrame(dict(a=[True,False], b=[True,True]),
index=['spam', 'ham'])
df.iloc[mask] = 999
</code></pre>
<p>那么<code>df</code>是</p>
^{pr2}$