如何根据其他列字符串为新列赋值？

import pandas as pd

# 创建一个示例数据集
data = {'A': ['apple,banana', 'orange,grape', 'pear,kiwi'],
        'B': ['fruit', 'fruit', 'fruit']}
df = pd.DataFrame(data)

# 根据列A和列B的字符串为列C赋值
df['C'] = ''

for index, row in df.iterrows():
    # 拆分列A的字符串
    fruits = row['A'].split(',')
    
    # 根据拆分后的字符串和列B的值来判断新值
    if row['B'] == 'fruit':
        if 'apple' in fruits:
            df.at[index, 'C'] = 'red'
        elif 'orange' in fruits:
            df.at[index, 'C'] = 'orange'
        else:
            df.at[index, 'C'] = 'unknown'
    else:
        df.at[index, 'C'] = 'unknown'

print(df)