days since last login -- pandas groupby cumulative count with reset

pandas-groupby-cumulative-count-with-reset.py

# for creating a column like "days since last login"

df = pd.read_clipboard(index_col=['customer_id', 'days'])
(df
 .groupby(level='customer_id')
 .did_login
 .cumsum()
 .to_frame()
 .groupby(level='customer_id')
 .apply(lambda g: g.groupby('did_login').cumcount())
)

Input:

customer_id days    did_login
2   -10 1
2   -9  1
2   -8  1
2   -7  1
2   -6  0
2   -5  0
2   -4  1
2   -3  0
2   -2  0
2   -1  0
2   0   1
8   -10 0
8   -9  1
8   -8  1
8   -7  1
8   -6  1
8   -5  0
8   -4  1
8   -3  1
8   -2  0
8   -1  0
8   0   0

Output:

2   2   -10 0
2   2   -9  0
2   2   -8  0
2   2   -7  0
2   2   -6  1
2   2   -5  2
2   2   -4  0
2   2   -3  1
2   2   -2  2
2   2   -1  3
2   2   0   0
8   8   -10 0
8   8   -9  0
8   8   -8  0
8   8   -7  0
8   8   -6  0
8   8   -5  1
8   8   -4  0
8   8   -3  0
8   8   -2  1
8   8   -1  2
8   8   0   3