擅长:python、mysql、java
<p>使用<a href="https://docs.scipy.org/doc/numpy/reference/generated/numpy.cumsum.html" rel="nofollow noreferrer">^{<cd1>}</a>或<code>pd.Series.cumsum</code>可以完美地处理数字和字符串:</p>
<pre><code>df['NewCol'] = df.groupby('colA')['colB'].apply(np.cumsum)
</code></pre>
<p>或:</p>
<pre><code>df['NewCol'] = df.groupby('colA')['colB'].apply(pd.Series.cumsum)
print (df)
colA colB NewCol
0 1 val1 val1
1 1 val2 val1val2
2 1 val3 val1val2val3
3 2 val4 val4
4 2 val5 val4val5
5 2 val6 val4val5val6
6 3 val7 val7
7 3 val8 val7val8
8 3 val9 val7val8val9
</code></pre>