Question

我需要在import cgi import cgitb; cgitb.enable() form = cgi.FieldStorage() serial_no = form.getvalue('serial') description = form.getvalue('description')到DataFrame的列中初始化单元格。

lists

我想知道在时间效率方面有更好的方法吗？

Answer 1

尝试apply：

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

样品：

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

因为您正在寻找时间效率，低于一些基准。我认为list理解已经非常快，可以创建空list个list个对象，但您可以使用itertools.repeat来缩小边际改进。在insert篇文章中，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dataframe列单元格初始化为空列表

2 个答案: