惹恼大熊猫 SettingWithCopyWarning，甚至尝试过 loc[;,]

Question

code_null.loc[:,'code'] = code_null['blockname'].apply(__f,args=(code_name,))

def __f(x, df):
    #markets = ['A','B']
    markets = ['A']
    for market in markets:
        code = df.loc[df.name==x,'code'].tolist()
    if code:
        return ','.join(code)
    else:
        return np.nan

总是收到SettingWithCopyWarning，

.virtualenv/python3/lib/python3.6/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

也试过了：

 code_null.loc[:,'code'] = code_null.loc[:,'blockname'].apply(__f,args=(code_name,))

但是收到了同样的警告。

Answer 1

尝试使用：

code_null.loc[:,(code)] = code_null[(blockname)].apply(__f,args=(code_name,))

复制方法不是首选：

.copy() 方法无法保证，应根据DOCS 避免使用

文档中的首选方法：

dfc = pd.DataFrame({'A':['aaa','bbb','ccc'],'B':[1,2,3]})

dfc.loc[0,'A'] = 11

dfc
     A  B
0   11  1
1  bbb  2
2  ccc  3

Answer 2

code_null.loc[:,'code'] = code_null['blockname'].apply(__f,args=(code_name,)).copy()