<p>将<a href="http://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.DataFrame.sort_values.html" rel="nofollow noreferrer">^{<cd1>}</a>与<a href="http://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.core.groupby.GroupBy.head.html" rel="nofollow noreferrer">^{<cd2>}</a>一起按2列使用:</p>
<pre><code>#if necessary
#df = df.groupby(['STATE','County'], as_index=False).sum()
df = df.sort_values(['STATE','POP'], ascending=[True, False]).groupby('STATE').head(3)
print (df)
STATE County POP
2 Alabama Baldwin County 182265
8 Alabama Calhoun County 118572
5 Alabama Blount County 57322
3164 Wisconsin Waukesha County 389891
3167 Wisconsin Winnebago County 166994
3163 Wisconsin Washington County 131887
3182 Wyoming Natrona County 75450
3186 Wyoming Sheridan County 29116
3184 Wyoming Park County 28205
</code></pre>
<p>如果需要<code>MultiIndex</code>添加<a href="http://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.DataFrame.set_index.html" rel="nofollow noreferrer">^{<cd4>}</a>:</p>
<pre><code>df = (df.sort_values(['STATE','POP'], ascending=[True, False])
.groupby('STATE')
.head(3)
.set_index(['STATE','County'])
</code></pre>