将组中的唯一值存储到Pandas中的另一列

import pandas as pd

data = {'A': [1, 2, 3, 2, 1, 3, 4, 5, 4]}
df = pd.DataFrame(data)

df['B'] = df['A'].drop_duplicates()

import pandas as pd

data = {'A': [1, 2, 3, 2, 1, 3, 4, 5, 4]}
df = pd.DataFrame(data)

df['B'] = df['A'].drop_duplicates()