如何将DataFrame中mth列的日期值提取为仅保留年份？

Hey there! Let's get your DataFrame's mth column simplified to just the year. Below are practical approaches based on what data type your mth column currently is:

Case 1: mth is already a datetime type #

If you've already converted the column to pandas datetime format, extracting the year is straightforward with the .dt.year accessor:

import pandas as pd

# Replace 'df' with your actual DataFrame name
df['mth'] = df['mth'].dt.year

Case 2: mth is a string type (e.g. '1977-01-01') #

If your dates are stored as strings, first convert them to datetime to ensure reliable year extraction (this handles most date format variations automatically):

# Convert string column to datetime, then extract year
df['mth'] = pd.to_datetime(df['mth']).dt.year

Example with your sample data #

Let's test this with a snippet of your data to see the result:

# Sample data matching your structure
sample_data = {
    'mth': ['1977-01-01', '1977-02-01', '2019-06-01'],
    'account_type': ['Special', 'Special', 'Special'],
    'interest_rate': [6.5, 6.5, 5]
}

df = pd.DataFrame(sample_data)
# Process the column
df['mth'] = pd.to_datetime(df['mth']).dt.year

print(df)

Output:

mth account_type  interest_rate
0  1977       Special            6.5
1  1977       Special            6.5
2  2019       Special            5.0

Note for custom date formats #

If your mth column uses a non-standard date format that pd.to_datetime() can't auto-detect, specify the format explicitly with the format parameter. For example, if dates were in 'DD-MM-YYYY' format:

df['mth'] = pd.to_datetime(df['mth'], format='%d-%m-%Y').dt.year

内容的提问来源于stack exchange，提问作者Lawrence How