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<p>我有两个具有多级索引r1和r2的数据帧，这样</p>
<pre><code>a1=['iso3_o', 'iso3_d', 'year', 'ExportFoodAndLiveAnimals']
a=np.array([['CAN', 'USA', '1995.0', '5918210.506'],
['CAN', 'USA', '1996.0', '6988508.727'],
['CAN', 'USA', '1997.0', '7792977.258'],
['CAN', 'USA', '1998.0', '8177456.631'],
['CAN', 'USA', '1999.0', '8773990.755'],
['CAN', 'USA', '2000.0', '9650783.071'],
['CAN', 'USA', '2001.0', '10800432.88'],
['CAN', 'USA', '2002.0', '11348837.38'],
['CAN', 'USA', '2003.0', '11313334.46'],
['CAN', 'USA', '2004.0', '12337588.35'],
['CAN', 'USA', '2005.0', '13227226.96'],
['CAN', 'USA', '2006.0', '14236699.34'],
['CAN', 'USA', '2007.0', '15638919.3'],
['CAN', 'USA', '2008.0', '17449901.08'],
['CAN', 'USA', '2009.0', '14813089.89'],
['CAN', 'USA', '2010.0', '16399733.82']])
r1 = pd.DataFrame(a, columns=a1)
r1
</code></pre>
<p>r2定义为</p>
^{pr2}$
<p>然后我决定加入他们的多索引级别</p>
<p>因此，我所做的是将列重置为索引</p>
<pre><code> multi_r2 = r2.set_index(['iso3_o', 'iso3_d','year'])
multi_r1 = r1.set_index(['iso3_o', 'iso3_d','year'])
df = multi_r2.join(multi_r1)
</code></pre>
<p>当我在“iso3”“o”，“iso3”“d”，“year”上加入时，数据帧df给了我一个NAN</p>
<p>为什么会这样？在</p>
<p>提前谢谢你</p>
