settingwithcopywarning: a value is trying to be set on a copy of a slice from a dataframe

"SettingWithCopyWarning" 是一种警告，表示您正在尝试在 DataFrame 的副本上设置值，而不是在原始 DataFrame 上设置值。这可能会导致错误或意外的结果，因此需要小心处理。解决这个问题的一种方法是使用 .loc 或 .iloc 来直接设置值，而不是使用类似 dataframe[condition] 的索引来设置值。

相关问题

SettingWithCopyWarning: A value is trying to be set on a copy of a slice from a DataFrame

This warning is raised when you try to modify a subset of a DataFrame obtained using indexing or slicing. When you use indexing or slicing to obtain a subset of a DataFrame, pandas returns a view of the original DataFrame rather than a new copy. If you try to modify this subset, pandas may not be able to determine whether you want to modify the original DataFrame or just the subset, which can lead to unexpected behavior.

To avoid this warning, you should use the `.loc` or `.iloc` accessor to modify the original DataFrame directly:

df.loc[indexer, column] = new_value

Alternatively, you can make a copy of the subset and modify the copy instead:

subset = df.loc[indexer, column].copy()
subset[column] = new_value
df.loc[indexer, column] = subset

By making a copy of the subset and modifying the copy, you avoid modifying the original DataFrame accidentally.

SettingWithCopyWarning: A value is trying to be set on a copy of a slice from a DataFrame

SettingWithCopyWarning是Pandas中的一个警告，它通常在我们使用链式索引时出现。这个警告的意思是我们正在尝试在一个数据切片的副本上进行修改，而不是原始数据上进行修改。这可能会导致我们的修改不生效或者影响到原始数据。为了避免这个问题，我们可以使用.loc或者.iloc函数来进行索引，或者在创建新数据时使用.copy()方法来明确告知Pandas创建一个副本。