SettingWithCopyWarning，使用loc

Question

我正在试着摆脱SettingWithCopyWarning。

我的代码：

combineQueryandBookFiltered['positionId'] = combineQueryandBookFiltered['positionId'].astype('int64')

combineQueryandBookFiltered.loc['pnlValue'] = np.multiply(combineQueryandBookFiltered['pnlValue'], df_fxrate['fx_rate'])

我尝试过的：

combineQueryandBookFiltered['positionId'] = combineQueryandBookFiltered['positionId'].astype('int64').copy()

combineQueryandBookFiltered.loc['pnlValue'] = np.multiply(combineQueryandBookFiltered['pnlValue'], df_fxrate['fx_rate'])

控制台消息：

//stack/over/flow/code1.py:154: 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: http://pandas.pydata.org/pandas-docs/stable/indexing.html#indexing-view-versus-copy
  combineQueryandBookFiltered['positionId'] = combineQueryandBookFiltered['positionId'].astype('int64').copy()
//stack/over/flow/code1:156: SettingWithCopyWarning: 
A value is trying to be set on a copy of a slice from a DataFrame

See the caveats in the documentation: http://pandas.pydata.org/pandas-docs/stable/indexing.html#indexing-view-versus-copy
  combineQueryandBookFiltered.loc['pnlValue'] = np.multiply(combineQueryandBookFiltered['pnlValue'], df_fxrate['fx_rate'])

有人可以帮助消除这些消息吗？

Answer 1

在导入pandas之后，您可以尝试在代码的开头运行此代码：

pd.options.mode.chained_assignment = None

然而，重要的是理解原因并解决它，而不是简单地抑制警告。你可以找到完整的解释here