1.set_index

DataFrame可以通過set_index方法，可以設置單索引和復合索引。 
DataFrame.set_index(keys, drop=True, append=False, inplace=False, verify_integrity=False) 
append添加新索引，drop為False，inplace為True時，索引將會還原為列

In [307]: data
Out[307]:
a b c d
0 bar one z 1.0
1 bar two y 2.0
2 foo one x 3.0
3 foo two w 4.0
In [308]: indexed1 = data.set_index('c')
In [309]: indexed1
Out[309]:
a b d
c
z bar one 1.0
y bar two 2.0
x foo one 3.0
w foo two 4.0
In [310]: indexed2 = data.set_index(['a', 'b'])
In [311]: indexed2
Out[311]:
c d
a b
bar one z 1.0
two y 2.0
foo one x 3.0
two w 4.0

2.reset_index

reset_index可以還原索引，重新變為默認的整型索引 
DataFrame.reset_index(level=None, drop=False, inplace=False, col_level=0, col_fill=”) 
level控制了具體要還原的那個等級的索引 
drop為False則索引列會被還原為普通列，否則會丟失

In [318]: data
Out[318]:
c d
a b
bar one z 1.0
two y 2.0
foo one x 3.0
two w 4.0
In [319]: data.reset_index()
Out[319]:
a b c d
0 bar one z 1.0
1 bar two y 2.0
2 foo one x 3.0
3 foo two w 4.0