<p>这是一个<a href="https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.wide_to_long.html" rel="nofollow noreferrer">^{<cd1>}</a>问题:</p>
<pre><code>pd.wide_to_long(df, stubnames=['date', 'val'], i='person_id', j='grp').sort_index(level=0)
</code></pre>
<hr/>
<pre><code> date val
person_id grp
1 1 12/31/2007 2
2 12/31/2017 1
3 12/31/2027 7
2 1 11/25/2009 4
2 11/25/2019 3
3 11/25/2029 9
3 1 10/06/2005 6
2 10/06/2015 5
3 10/06/2025 11
</code></pre>
<hr/>
<p>要匹配预期输出:</p>
<pre><code>df = pd.wide_to_long(df, stubnames=['date', 'val'], i='person_id', j='grp').sort_index(level=0)
df = df.reset_index(level=1, drop=True).reset_index()
</code></pre>
<hr/>
<pre><code> person_id date val
0 1 12/31/2007 2
1 1 12/31/2017 1
2 1 12/31/2027 7
3 2 11/25/2009 4
4 2 11/25/2019 3
5 2 11/25/2029 9
6 3 10/06/2005 6
7 3 10/06/2015 5
8 3 10/06/2025 11
</code></pre>