如何将DataFrame的‘Date of birth’列格式化为仅日期格式？

Hey there! Let's sort out your date formatting issue and set you up for calculating ages smoothly.

First, let's break down why your original code didn't work:

• The format='%d%b%Y' in pd.to_datetime() is designed for dates like 30Apr1957, but your raw data uses the standard ISO format YYYY-MM-DD HH:MM:SS—so specifying that format caused a mismatch.
• The second line converts dates to a MM/DD/YYYY string, which isn't the YYYY-MM-DD format you want, and converting to strings can make age calculations harder later.

Step 1: Convert to Datetime Type (Correctly) #

First, ensure your column is properly parsed as datetime. Since your data is already in a standard format, you don't need the format parameter at all:

import pandas as pd

# Parse the column to datetime (automatically handles the ISO format)
df["Date of birth"] = pd.to_datetime(df["Date of birth"])

Step 2: Get Pure Date Format (Two Options) #

Choose based on your needs:

1. Keep as Datetime Type (best for age calculations)
   This removes the time component but keeps the column as a datetime dtype, which is ideal for date arithmetic:

   # Remove time component (sets time to 00:00:00 but keeps datetime type)
   df["Date of birth"] = df["Date of birth"].dt.normalize()
   # Alternative: use floor to day
   # df["Date of birth"] = df["Date of birth"].dt.floor("D")
   

   When you print the DataFrame, it will display just the date (e.g., 1957-04-30) instead of the full timestamp.

2. Convert to String (YYYY-MM-DD)
   If you specifically need a string column in that exact format:

   df["Date of birth"] = df["Date of birth"].dt.strftime("%Y-%m-%d")
   

Step 3: Calculate Age from Birth Date #

Now that your dates are properly formatted, here's how to calculate age accurately (accounting for whether the person has had their birthday this year):

from datetime import datetime

def calculate_age(birth_date):
    today = datetime.today()
    age = today.year - birth_date.year
    # Subtract 1 if birthday hasn't occurred yet this year
    if (today.month, today.day) < (birth_date.month, birth_date.day):
        age -= 1
    return age

# Apply the function (works if "Date of birth" is datetime type)
df["Age"] = df["Date of birth"].apply(calculate_age)

That should get you exactly the formatted dates you want, plus a reliable age calculation!

内容的提问来源于stack exchange，提问作者Stacey