将 Pandas DataFrame 切片为新的 DataFrame
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Slicing a Pandas DataFrame into a new DataFrame
提问by Pietro Marchesi
I would like to slice a DataFrame with a Boolean index obtaining a copy, and then do stuff on that copy independently of the original DataFrame.
我想使用布尔索引对 DataFrame 进行切片以获得副本，然后在该副本上独立于原始 DataFrame 执行操作。
Judging from this answer, selecting with .locusing a Boolean array will hand me back a copy, but then, if I try to change the copy, SettingWithCopyWarninggets in the way. Would this then be the correct way:
从这个答案来看，选择.loc使用布尔数组会给我一个副本，但是，如果我尝试更改副本，SettingWithCopyWarning就会妨碍我。那么这是否是正确的方法：
import numpy as np
import pandas as pd
d1 = pd.DataFrame(np.random.randn(10, 5), columns=['a', 'b', 'c', 'd', 'e'])
# create a new dataframe from the sliced copy
d2 = pd.DataFrame(d1.loc[d1.a > 1, :])
# do stuff with d2, keep d1 unchanged
回答by jezrael
You need copywith boolean indexing, new DataFrameconstructor is not necessary:
您需要copywith boolean indexing，不需要新的DataFrame构造函数：
d2 = d1[d1.a > 1].copy()
Explanation of warning:
警告说明：
If you modify values in d2later you will find that the modifications do not propagate back to the original data (d1), and that Pandas does warning.
如果d2稍后修改值，您会发现修改不会传播回原始数据 ( d1)，并且 Pandas 会发出警告。
