擅长:python、mysql、java
<p>您可以使用<code>value_counts</code>和<code>head</code>:</p>
<pre><code>s = df.groupby('Group')['Name'].apply(lambda x: x.value_counts().head(1)).reset_index(-1)['level_1']
df['Name'] = df['Name'].fillna(df['Group'].map(s))
print(df)
</code></pre>
<p>输出:</p>
<pre><code> Group Name
0 1 Annie
1 2 Bertha
2 3 Chris
3 4 David
4 1 Annie
5 2 Bertha
6 3 Chris
7 4 David
</code></pre>