title: Python: SettingWithCopyWarning: A value is trying to be set on a copy of a slice from a DataFrame
body: <p>My pandas dataframe:</p>
  
  <pre><code>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
  </code></pre>
  
  <p>My desired output:</p>
  
  <pre><code>    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
  </code></pre>
  
  <p>Idea is to create new column based on values in 'B' column, copy respective values in 'C' column and paste them in newly created columns. 
  Here is my code:</p>
  
  <pre><code>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]
  </code></pre>
  
  <p>I ended up with this error:</p>
  
  <pre><code>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()
  </code></pre>
  
  <p>This code worked well in Python 2.7 but not in 3.x. Where I'm going wrong?</p>