创建新列时如何使用.loc

Question

df.loc[:,'C'] = df.apply(lambda row: min(row['A'],row['B']) if row['A'] > 0 else max(row['B'],0),axis=1)

我正在数据帧df中创建一个新变量'C'。尽管使用.loc函数，但出现了切片错误。我该如何解决？

/opt/python/python35/lib/python3.5/site-packages/pandas/core/indexing.py:362: 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[key] = _infer_fill_value(value)
/opt/python/python35/lib/python3.5/site- 
packages/pandas/core/indexing.py:543: 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

Answer 1

链接到文档loc

df.loc[:,'C']=df.apply(lambda row: min(row['A'],row['B']) if row['A'] > 0 else max(row['B'],0),axis=1)