对 Pandas 数据帧切片进行排序的正确方法

Question

I'm new to Pandas, and constantly getting the infamous SettingWithCopyWarning. If I have code like the following I get the warning:

import pandas as pd
import numpy as np

t1 = pd.DataFrame({'A':np.random.randn(8), 'B': np.random.randint(0,4,8)})

table = t1[t1['B'] < 3]

print(table)

table.sort(['B'], inplace=True)

print(table)

1. In this case, is it just warning me that the original data frame (ie, 't1') will not be sorted when I run the sort?

2. Is there a more accepted way to perform this sort of operation (getting a slice of a data frame, and then applying functions on that slice)?

Answer 1

Why not make a copy of the slice? Then you will not have the warning.

a = table.copy()

You can read more in the answers to this post How to deal with SettingWithCopyWarning in Pandas? .

Answer 2

You can also avoid to use inplace , in this case the copy will be made behind the scene for you.

t1 = pd.DataFrame({'A':np.random.randn(8), 'B': np.random.randint(0,4,8)})
table = t1[t1['B'] < 3]
table = table.sort(['B'])
print(table)