从此样本数据开始...
import pandas as pd
start_data = {"person_id": [1, 1, 1, 1, 2], "nid": [1, 2, 3, 4, 1],
"beg": ["Jan 1 2018", "Jan 5 2018", "Jan 10 2018", "Feb 5 2018", "Jan 25 2018"],
"end": ["Feb 1 2018", "Mar 4 2018", "", "Oct 18 2018", "Nov 10 2018"]}
df = pd.DataFrame(start_data)
df["beg"] = pd.to_datetime(df["beg"])
df["end"] = pd.to_datetime(df["end"])
初始点：
person_id nid beg end
0 1 1 2018-01-01 2018-02-01
1 1 2 2018-01-05 2018-03-04
2 1 3 2018-01-10 NaT
3 1 …