这对我来说很管用:

import pandas as pd
import numpy as np
future = pd.DataFrame(
    pd.date_range('2022-09-01',periods=360),
    columns=['date']
)

def featurize(datetime):
    return pd.Series({
        'month':datetime.month,
        'year':datetime.year,
        'dayofweek':datetime.dayofweek,
        'dayofyear':datetime.dayofyear
    })
    
future.loc[
    :,['month','year','dayofweek','dayofyear']
    ] = future.date.apply(featurize)

future.head()

输出:

    date    month   year    dayofweek   dayofyear
0   2022-09-01  9   2022    3           244
1   2022-09-02  9   2022    4           245
2   2022-09-03  9   2022    5           246
3   2022-09-04  9   2022    6           247
4   2022-09-05  9   2022    0           248

只需使用result_type="expand"

df = pd.DataFrame(np.random.randint(0,10,(10,2)), columns=["random", "a"])
df[["sq_a","cube_a"]] = df.apply(lambda x: [x.a**2, x.a**3], axis=1, result_type="expand")

对于95%的用例来说，这是正确且最简单的方法:

>>> df = pd.DataFrame(zip(*[range(10)]), columns=['num'])
>>> df
    num
0    0
1    1
2    2
3    3
4    4
5    5

>>> def example(x):
...     x['p1'] = x['num']**2
...     x['p2'] = x['num']**3
...     x['p3'] = x['num']**4
...     return x

>>> df = df.apply(example, axis=1)
>>> df
    num  p1  p2  p3
0    0   0   0    0
1    1   1   1    1
2    2   4   8   16
3    3   9  27   81
4    4  16  64  256

在2020年，我使用apply()参数result_type='expand'

applied_df = df.apply(lambda row: fn(row.text), axis='columns', result_type='expand')
df = pd.concat([df, applied_df], axis='columns')

在另外两个类似的问题上也有相同的答案。我更喜欢这样做的方式是将函数的返回值打包成一个系列:

def f(x):
    return pd.Series([x**2, x**3])

然后使用apply创建单独的列，如下所示:

df[['x**2','x**3']] = df.apply(lambda row: f(row['x']), axis=1)

公认的解决方案对于大量数据来说将会非常慢。获得最多赞数的解决方案读起来有点困难，而且处理数字数据也很慢。如果每个新列都可以独立于其他列计算，那么我将直接分配它们，而不使用apply。

假字符数据的例子

在DataFrame中创建100,000个字符串

df = pd.DataFrame(np.random.choice(['he jumped', 'she ran', 'they hiked'],
                                   size=100000, replace=True),
                  columns=['words'])
df.head()
        words
0     she ran
1     she ran
2  they hiked
3  they hiked
4  they hiked

假设我们想提取一些文本特征，就像在最初的问题中所做的那样。例如，让我们提取第一个字符，计算字母“e”的出现次数，并将短语大写。

df['first'] = df['words'].str[0]
df['count_e'] = df['words'].str.count('e')
df['cap'] = df['words'].str.capitalize()
df.head()
        words first  count_e         cap
0     she ran     s        1     She ran
1     she ran     s        1     She ran
2  they hiked     t        2  They hiked
3  they hiked     t        2  They hiked
4  they hiked     t        2  They hiked

计时

%%timeit
df['first'] = df['words'].str[0]
df['count_e'] = df['words'].str.count('e')
df['cap'] = df['words'].str.capitalize()
127 ms ± 585 µs per loop (mean ± std. dev. of 7 runs, 10 loops each)

def extract_text_features(x):
    return x[0], x.count('e'), x.capitalize()

%timeit df['first'], df['count_e'], df['cap'] = zip(*df['words'].apply(extract_text_features))
101 ms ± 2.96 ms per loop (mean ± std. dev. of 7 runs, 10 loops each)

令人惊讶的是，通过遍历每个值可以获得更好的性能

%%timeit
a,b,c = [], [], []
for s in df['words']:
    a.append(s[0]), b.append(s.count('e')), c.append(s.capitalize())

df['first'] = a
df['count_e'] = b
df['cap'] = c
79.1 ms ± 294 µs per loop (mean ± std. dev. of 7 runs, 10 loops each)

另一个假数字数据的例子

创建100万个随机数并从上面测试幂函数。

df = pd.DataFrame(np.random.rand(1000000), columns=['num'])


def powers(x):
    return x, x**2, x**3, x**4, x**5, x**6

%%timeit
df['p1'], df['p2'], df['p3'], df['p4'], df['p5'], df['p6'] = \
       zip(*df['num'].map(powers))
1.35 s ± 83.6 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)

为每一列赋值速度快25倍，可读性强:

%%timeit 
df['p1'] = df['num'] ** 1
df['p2'] = df['num'] ** 2
df['p3'] = df['num'] ** 3
df['p4'] = df['num'] ** 4
df['p5'] = df['num'] ** 5
df['p6'] = df['num'] ** 6
51.6 ms ± 1.9 ms per loop (mean ± std. dev. of 7 runs, 10 loops each)

我在这里也做了类似的回答，并详细说明了为什么申请通常不是正确的选择。