python - Pandas: Multilevel column names

Question

pandas has support for multi-level column names:

>>>  x = pd.DataFrame({'instance':['first','first','first'],'foo':['a','b','c'],'bar':rand(3)})
>>> x = x.set_index(['instance','foo']).transpose()
>>> x.columns
MultiIndex
[(u'first', u'a'), (u'first', u'b'), (u'first', u'c')]
>>> x
instance     first                    
foo              a         b         c
bar       0.102885  0.937838  0.907467

This feature is very useful since it allows multiple versions of the same dataframe to be appended 'horizontally' with the 1st level of the column names (in my example instance) distinguishing the instances.

Imagine I already have a dataframe like this:

                 a         b         c
bar       0.102885  0.937838  0.907467

Is there a nice way to add another level to the column names, similar to this for row index:

x['instance'] = 'first'
x.set_level('instance',append=True)

question from:https://stackoverflow.com/questions/21443963/pandas-multilevel-column-names

Answer 1

Try this:

df=pd.DataFrame({'a':[1,2,3],'b':[4,5,6]})

columns=[('c','a'),('c','b')]

df.columns=pd.MultiIndex.from_tuples(columns)