pandas 将数据框列单元格初始化为空列表

Question

我需要将DataFrame列中的单元格初始化为lists。

df['some_col'] = [[] for _ in no_of_rows]

我想知道在时间效率方面是否有更好的方法？

Answer 1

尝试 apply:

df1['some_col'] = ''
df1['some_col'] = df1['some_col'].apply(list)

样本：

df1 = pd.DataFrame({'a': pd.Series([1,2])})
print (df1)
   a
0  1
1  2

df1['some_col'] = ''
df1['some_col'] = df1['some_col'].apply(list)
print (df1)
   a some_col
0  1       []
1  2       []

Answer 2

由于您正在寻找时间效率，低于一些基准。我认为 list 理解创建空的 list of list 对象已经相当快了，但是你可以使用 itertools.repeat 挤出边际改进。在 insert 部分，apply 慢了 3 倍，因为它循环：

import pandas as pd
from itertools import repeat
df = pd.DataFrame({"A":np.arange(100000)})

%timeit df['some_col'] = [[] for _ in range(len(df))]
100 loops, best of 3: 8.75 ms per loop

%timeit df['some_col'] = [[] for i in repeat(None, len(df))]
100 loops, best of 3: 8.02 ms per loop

%%timeit 
df['some_col'] = ''
df['some_col'] = df['some_col'].apply(list)
10 loops, best of 3: 25 ms per loop

pandas 将数据框列单元格初始化为空列表

pandas initialize dataframe column cells as empty lists

python

series

dataframe

python-3.x

pandas