擅长:python、mysql、java
<p>尝试:</p>
<pre><code>df['Total_B'] = (df['Definition'].eq('B').mul(df['Total_to_Add'])
.groupby(df['Ref_No']).transform('sum'))
</code></pre>
<p>[输出]</p>
<pre><code> Ref_No Definition Total_to_Add Total_B
0 ref1 B 20 240
1 ref2 A 30 100
2 ref1 B 40 240
3 ref2 A 50 100
4 ref1 B 60 240
5 ref2 B 50 100
6 ref1 B 60 240
7 ref2 B 50 100
8 ref1 B 60 240
</code></pre>