Pandas Join创建了不需要的副本，只需要第一个实例

import pandas as pd
dict1 = {
'State': ['CA', 'NY', 'NJ'],
'PS': [0, 0, 1]
}
dict2 = {
'Study': ['Active', 'Active', 'Closed'],
}
df1 = pd.DataFrame(data=dict1, index=[1001, 1002, 1003])
df2 = pd.DataFrame(data=dict2, index=[1001, 1002, 1002])
print(df1)
print(df2)
answer = df1.join(df2).drop_duplicates(subset=['State', 'PS'], keep='first')
print(answer)

关键的是，drop_duplicate方法应该能够处理这种特殊情况