python - 条件为真开始计数，直到下一行为真重新开始计数

Question

预期结果表

    bool    count
0   FALSE   
1   FALSE   
2   TRUE    0
3   FALSE   1
4   FALSE   2
5   FALSE   3
6   TRUE    0
7   FALSE   1
8   TRUE    0
9   TRUE    0

如何计算'count'列的值

Answer 1

给你:

# create bool dataframe
df = pd.DataFrame(dict(bool_= [0, 0, 1, 0, 0, 1, 1, 0, 0, 0]), dtype= bool)
df.index = list("abcdefghij")

# create a new Series unique integers to associate a group for the rows
# between True values
ix = pd.Series(range(df.shape[0])).where(df.bool_.values, np.nan).ffill().values

# if the first rows are False, they will be NaNs and shouldn't be 
# counted so only perform groupby and cumcount() for what is notna
notna = pd.notna(ix)
df["count"] = df[notna].groupby(ix[notna]).cumcount()

>>> df   
   bool_  count
a  False    NaN
b  False    NaN
c   True    0.0
d  False    1.0
e  False    2.0
f   True    0.0
g   True    0.0
h  False    1.0
i  False    2.0
j  False    3.0