Pandas DataFrame:SettingWithCopyWarning:试图在DataFrame的切片副本上设置一个值 [英] Pandas DataFrame: SettingWithCopyWarning: A value is trying to be set on a copy of a slice from a DataFrame

问题描述

我知道关于此警告的帖子很多，但是我找不到解决我的情况的解决方案.这是我的代码:

I know there are tons of posts about this warning, but I couldn't find a solution to my situation. Here's my code:

df.loc[:, 'my_col'] = df.loc[:, 'my_col'].astype(int)
#df.loc[:, 'my_col'] = df.loc[:, 'my_col'].astype(int).copy()
#df.loc[:, 'my_col'] = df['my_col'].astype(int)

它会产生警告:

SettingWithCopyWarning:试图在一个副本上设置一个值 从DataFrame切片.尝试使用.loc [row_indexer，col_indexer] = 值代替

SettingWithCopyWarning: A value is trying to be set on a copy of a slice from a DataFrame. Try using .loc[row_indexer,col_indexer] = value instead

即使我按建议更改了代码，仍然收到此警告?我需要做的就是转换一列的数据类型.

Even though I changed the code as suggested, I still get this warning? All I need to do is to convert the data type of one column.

**备注:**最初，该列是float类型，具有一个小数点(例如:4711.0).因此，我将其更改为整数(4711)，然后更改为字符串('4711')-只是为了删除小数.

**Remark: ** Originally the column is of type float having one decimal (example: 4711.0). Therefore I change it to integer (4711) and then to string ('4711') - just to remove the decimal.

感谢您的帮助！

更新:警告是对之前进行的原始数据过滤的副作用.我错过了DataFrame.copy().改用副本即可解决问题！

Update: The warning was a side effect on a filtering of the original data that was done just before. I was missing the DataFrame.copy(). Using the copy instead, solved the problem!

df = df[df['my_col'].notnull()].copy()
df.loc[:, 'my_col'] = df['my_col'].astype(int).astype(str)
#df['my_col'] = df['my_col'].astype(int).astype(str) # works too!

推荐答案

我认为需要 说明:

如果以后在df中修改值，您会发现修改不会传播回原始数据(df)，并且Pandas会发出警告.

If you modify values in df later you will find that the modifications do not propagate back to the original data (df), and that Pandas does warning.

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