SettingWithCopyWarning与.loc

Question

此代码生成SettingWithCopyWarning如下所示：

raw_corpus.loc[:,'constructed_recipe']=raw_corpus.loc[:,'trigger_channel_cat'] + " " + raw_corpus.loc[:,'trigger_channel_clean'] + " " + raw_corpus.loc[:,'trigger_name_clean'] + " " + raw_corpus.loc[:,'action_name_clean'] +" " + raw_corpus.loc[:,'action_channel_clean'] +" " + raw_corpus.loc[:,'action_channel_cat']

/Users/dlhoffman/anaconda3/envs/gensim-py35/lib/python3.5/site-packages/pandas/core/indexing.py:537: 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
  self.obj[item] = s

此代码生成一个不同的警告：

raw_corpus['constructed_recipe']=raw_corpus['trigger_channel_cat'] + " " + raw_corpus['trigger_channel_clean'] + " " + raw_corpus['trigger_name_clean'] + " " + raw_corpus['action_name_clean'] +" " + raw_corpus['action_channel_clean'] +" " + raw_corpus['action_channel_cat']

/Users/dlhoffman/anaconda3/envs/gensim-py35/lib/python3.5/site-packages/ipykernel_launcher.py:5: 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
"""

这两段代码都可以做我想做的事情，但是这个错误很烦人，我的理解是这不是一个很好的错误。我已经阅读了文档和这里的人们的建议，但我不知道我做错了什么。

Answer 1

这是一个有充分记录的错误。看看How to deal with SettingWithCopyWarning in Pandas?。

要解决这个问题，先从

raw_corpus = raw_corpus.copy(deep=True)

接下来，获取要聚合的所有列的列表：

cols = ['trigger_channel_cat', 'trigger_channel_clean', ...]

打电话给df.agg

raw_corpus['constructed_recipe'] = raw_corpus[cols].agg(' '.join, axis=1)