获取分层pandas数据帧中的先前值

import pandas as pd

# 创建一个示例数据帧
data = {
    'group': ['A', 'A', 'B', 'B', 'A', 'B'],
    'time': [1, 2, 1, 2, 3, 3],
    'value': [10, 20, 30, 40, 50, 60]
}
df = pd.DataFrame(data)

# 按'group'和'time'排序
df = df.sort_values(by=['group', 'time'])

# 使用shift()获取先前值
df['previous_value'] = df.groupby('group')['value'].shift(1)

print(df)

  group  time  value  previous_value
0     A     1     10             NaN
1     A     2     20            10.0
4     A     3     50            20.0
2     B     1     30             NaN
3     B     2     40            30.0
5     B     3     60            40.0

# 填充NaN值
df['previous_value'] = df.groupby('group')['previous_value'].fillna(method='ffill')