Python：SettingWithCopyWarning：尝试在DataFrame的切片副本上设置值

我的熊猫数据帧：

dframe = pd.DataFrame({"A":list("abcde"),"B":list("aabbc"),"C":[1,2,3,4,5]},index=[10,11,12,13,14])

    A   B   C
10  a   a   1
11  b   a   2
12  c   b   3
13  d   b   4
14  e   c   5

我想要的输出：

A   B   C   a   b   c
10  a   a   1   1   None    None
11  b   a   2   2   None    None
12  c   b   3   None    3   None
13  d   b   4   None    4   None
14  e   c   5   None    None    5

想法是根据“B”列中的值创建新列,复制“C”列中的相应值并将其粘贴到新创建的列中.
这是我的代码：

lis = sorted(list(dframe.B.unique()))

#creating empty columns
for items in lis:
   dframe[items] = None


 #here copy and pasting
    for items in range(0,len(dframe)):
        slot = dframe.B.iloc[items]
        dframe[slot][items] = dframe.C.iloc[items]

我最终得到了这个错误：

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
  app.launch_new_instance()

此代码在Python 2.7中运行良好,但在3.x中运行不佳.我哪里错了？

解决方法

从…开始

to_be_appended = pd.get_dummies(dframe.B).replace(0,np.nan).mul(dframe.C,axis=0)

然后结束

dframe = pd.concat([dframe,to_be_appended],axis=1)

好像：

print dframe

    A  B  C    a    b    c
10  a  a  1  1.0  NaN  NaN
11  b  a  2  2.0  NaN  NaN
12  c  b  3  NaN  3.0  NaN
13  d  b  4  NaN  4.0  NaN
14  e  c  5  NaN  NaN  5.0

搜索注意事项.

这是将一个热编码与广播乘法相结合.