如何仅从Pandas中的前20个唯一日期(其实例计数不相等)中选择所有列值

import pandas as pd

df = pd.DataFrame({'日期': ['2022-01-01', '2022-01-01', '2022-01-02', '2022-01-03', '2022-01-03', '2022-01-04', '2022-01-05', '2022-01-06', '2022-01-07', '2022-01-08', '2022-01-09', '2022-01-10', '2022-01-11', '2022-01-12', '2022-01-13', '2022-01-14', '2022-01-15', '2022-01-16', '2022-01-17', '2022-01-18', '2022-01-19']})

df['日期'] = pd.to_datetime(df['日期'])

unique_dates = df['日期'].unique()[:20]

selected_rows = df[df['日期'].isin(unique_dates)]