如何使用现有列上的条件在Dataframe中创建新列？

import pandas as pd

# 创建一个示例DataFrame
data = {'A': [1, 2, 3, 4],
        'B': [10, 20, 30, 40]}
df = pd.DataFrame(data)

# 使用apply()和lambda表达式创建新列'C'
df['C'] = df['A'].apply(lambda x: 'even' if x % 2 == 0 else 'odd')

print(df)

# 使用条件表达式创建新列'C'
df['C'] = ['even' if x % 2 == 0 else 'odd' for x in df['A']]

print(df)

import numpy as np

# 使用numpy.where()创建新列'C'
df['C'] = np.where(df['A'] % 2 == 0, 'even', 'odd')

print(df)

# 使用loc创建新列'C'
df.loc[df['A'] % 2 == 0, 'C'] = 'even'
df.loc[df['A'] % 2 != 0, 'C'] = 'odd'

print(df)

# 使用np.select()处理多个条件
conditions = [
    (df['A'] % 2 == 0),
    (df['A'] > 2)
]
choices = ['even', 'greater_than_two']
df['D'] = np.select(conditions, choices, default='other')

print(df)