擅长:python、mysql、java
<p>试试这个:</p>
<pre><code>df = pd.DataFrame({'id' : [1234, 1235, 1236], 'name' : ['R', 'Python', 'Pandas']})
id name
0 1234 R
1 1235 Python
2 1236 Pandas
df1 = pd.DataFrame({'id' : [1234, 1234, 1234, 1234, 1234, 1235, 1235, 1236], 'amount' : [1, 1, 2, 1, 2, 2, 1, 1]})
amount id
0 1 1234
1 1 1234
2 2 1234
3 1 1234
4 2 1234
5 2 1235
6 1 1235
7 1 1236
df['quantity'] = df1.groupby('id').agg(sum).values
id name quantity
0 1234 R 7
1 1235 Python 3
2 1236 Pandas 1
</code></pre>