每次出现0时重置的Python pandas cumsum [英] Python pandas cumsum with reset everytime there is a 0

问题描述

我有一个0和1的矩阵，并且想对每列进行一次累加，每当观察到零时就将其重置为0.例如，如果我们有以下内容:

I have a matrix with 0s and 1s, and want to do a cumsum on each column that resets to 0 whenever a zero is observed. For example, if we have the following:

df = pd.DataFrame([[0,1],[1,1],[0,1],[1,0],[1,1],[0,1]],columns = ['a','b'])
print(df)
   a  b
0  0  1
1  1  1
2  0  1
3  1  0
4  1  1
5  0  1

我想要的结果是:

print(df)
   a  b
0  0  1
1  1  2
2  0  3
3  1  0
4  2  1
5  0  2

但是，当我尝试df.cumsum() * df时，我能够正确识别0个元素，但计数器不会重置:

However, when I try df.cumsum() * df, I am able to correctly identify the 0 elements, but the counter does not reset:

print(df.cumsum() * df)
   a  b
0  0  1
1  1  2
2  0  3
3  2  0
4  3  4
5  0  5

推荐答案

您可以使用:

a = df != 0
df1 = a.cumsum()-a.cumsum().where(~a).ffill().fillna(0).astype(int)
print (df1)
   a  b
0  0  1
1  1  2
2  0  3
3  1  0
4  2  1
5  0  2

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