擅长:python、mysql、java
<p>IIUC您需要:</p>
<pre><code>df.merge(df.groupby('id')['c1'].apply(lambda x : x.max()).reset_index().rename(columns={'c1':'c1_secondLargest'}),on='id')
</code></pre>
<p>或:</p>
<pre><code>print(df.merge(df.groupby('id')['c1'].apply(lambda x : x.nlargest(1)).reset_index().rename(columns={'c1':'c1_secondLargest'}).drop('level_1',axis=1),on='id'))
id c1 c1_secondLargest
0 1 3 75
1 1 34 75
2 1 75 75
3 2 84 96
4 2 54 96
5 2 23 96
6 2 96 96
7 3 55 76
8 3 76 76
</code></pre>