相关疑难解决方法(0)

从父数据帧中选择子数据帧时,我注意到一些程序员使用该.copy()方法复制数据帧.

他们为什么要复制数据框？如果我不复制会怎么样？

我有一个 Pandas DataFrame，我想用以下代码更改列的所有值：

df["Population"] = round(df["Population"]/1000000,1)

我收到以下警告：

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

See the caveats in the documentation: https://pandas.pydata.org/pandas-docs/stable/user_guide/indexing.html#returning-a-view-versus-a-copy
  return super().rename(
<ipython-input-6-59bf041bb022>:2: 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

See the caveats in the documentation: https://pandas.pydata.org/pandas-docs/stable/user_guide/indexing.html#returning-a-view-versus-a-copy
  df["Population"] = round(df["Population"]/1000000,1)

正确的做法是什么并避免此类警告？

感谢您的帮助！