Python函数，用于在数据框中选择最接近所选时间的日值

import pandas as pd

def select_nearest_date(df, selected_date):
    # 将日期列转换为datetime类型
    df['日期'] = pd.to_datetime(df['日期'])
    
    # 计算每个日期与所选日期的差值
    df['差值'] = abs(df['日期'] - selected_date)
    
    # 找到最小差值对应的行
    nearest_row = df.loc[df['差值'].idxmin()]
    
    # 返回最接近日期的日值
    return nearest_row['日值']

# 创建一个示例数据框
data = {'日期': ['2022-01-01', '2022-01-02', '2022-01-03', '2022-01-04'],
        '日值': [10, 20, 30, 40]}
df = pd.DataFrame(data)

# 选择最接近2022-01-03的日值
selected_date = pd.to_datetime('2022-01-03')
nearest_day = select_nearest_date(df, selected_date)
print(nearest_day)

30